Mass Effect is the most beautiful dice roll you never saw. It is an illusion, a picture perfect disguise, one that makes the foundations upon which role playing games are built - statistics, levelling up, character development - dissolve in an HD gust of wind. Because of this Mass Effect transcends its genre - a genre that began with a notepad, pen and dice all those years ago - and fully deserves its rightful place in the pantheon of science-fiction entertainment.

BioWare, Mass Effect's creator, must now be considered the greatest sci-fi RPG developer of modern times. It has taken its already critically acclaimed Knights of the Old Republic games, stripped away the Star Wars license, drowned them in a tsunami of next-generation polish and given me what can only be described as one of the finest video game experiences I've ever had.

That is not to say that BioWare's work with KotOR has been forgotten. Reminders of the series whisper in your mind as the Mass Effect universe takes its hold. From its game mechanics to the way it allows you to mould your experience like virtual clay, Mass Effect is KotOR refined - re-imagined for the masses - it is the result of a decision to make the best possible RPG for as many people as possible, even those who might otherwise have passed the genre by.

And the game's superb plot, told through some of the best voice acting we've ever heard (there are some famous voices in there, including the Arbiter from Halo) leads from the front. The game begins aboard the Human Alliance space ship the Normandy, where Captain Anderson and the Turian, Nihlus, are debating whether Commander Shepard, aka you, is ready to become the first human Spectre, a kind of all powerful galaxy commando, and not unlike a Jedi. Your first mission is on Eden Prime, a peaceful paradise planet settled by humans. A beacon built by the now extinct Protheans, an alien race responsible for the Citadel, a planet-sized space installation and the Mass relays, which allow travel across the galaxy, has been discovered there. Nihlus, himself a Spectre, wants to experience your skills first hand to see if you're ready for the role.

Things go wrong pretty quickly. The Normandy receives a distress transmission from Eden Prime detailing an attack by a giant, claw-like space ship. You and two other squad members investigate the dig site, fighting your way past alien robots called the Geth. You finally catch up with Nihlus who has been murdered by a fellow turian Spectre called Saren. Turns out Saren's gone rogue and is commanding the Geth. He steals the beacon, but not before it imprints in your brain a vision of death and destruction. He escapes in the giant claw-like ship, Sovereign, that you saw in the transmission. It's now up to you to chase him across the galaxy, reveal his true motives and unravel the mystery behind the vision and the mysterious Prothean beacon. While we won't spoil the story for you, (relax, the ending is superb) what we will say is that playing Mass Effect is a bit like watching your favourite ever sci-fi film - except this time you're the star and the director.

Mass Effect is full of brilliant touches that help make it feel less hardcore RPG and more fast-flowing action game. Example one: the combat, which is absolute genius. Mass Effect's combat feels like Epic's blockbuster Gears of War. You've got a third-person camera angle, a targeting reticule, squad commands, a roadie run and even a cover system (doesn't everything these days) from which you can pop out, zoom in and hit a space mutant between the eyes with a well placed pulse from your sniper rifle. But don't be fooled - this isn't Gears of War. The dice is still being cast, it's just wonderfully disguised. Your chance to hit is being worked out from behind the camera. The percentage likelihood that your bullet, your tech ability or your biotic power will penetrate your enemy's shield and score deep into its flesh is the result of countless calculations worked out in real-time behind the scenes. No need to pause, no need to understand the why behind it all.

Mass Effect's story is one of the best we've seen

Sure you can micro-manage your squad if you want, pausing after every action to pick and direct special abilities from within the game's excellent power wheel, but the point is you don't have to. Your squad works perfectly well if you simply leave them alone to get on with the job and very rarely do they do a stupid thing or get in the way. Apart from the odd AI issue with them not being able to move across to certain positions despite clearly being able to, whatever two team members you choose to accompany you on missions you'll find that they never annoy, which is the most important thing. This is one of Mass Effect's greatest triumphs - to wrap KotOR in a fully functional and fantastically fun action shooter's robes. So good is the disguise that it was an effort for me to stop thinking like Marcus Fenix and start thinking like Commander Shepard.

Example two: the conversation system. Despite the hype, Mass Effect's conversation system is not revolutionary. It does not allow you to interrupt other game characters mid sentence, nor does it break any boundaries by making possible even remotely realistic dialogue - it's still question, answer, question, answer. But what it does do is burn away the inefficiency and fluff of previous efforts, leaving behind a simple, gloriously cinematic and intuitive way of interacting with computer controlled characters. You know you have a special RPG on your hands when you want to talk to people, and in Mass Effect that's exactly what you've got. It is a medium through which you can role play without hindrance, whether it is as a hard-nosed bitch, one that will do anything to get the job done, or as a do-gooder. And it all looks stunning, with dynamic camera angles, incredibly detailed facial animations and impressive textures.

The conversation system isn't revolutionary, but it's sweet to use

With simple flicks of the analogue stick you can shape conversations to your own play style, choosing what to say a few seconds before the other character has finished. Where dialogue options appear on the wheel determines their effect. Choices that appear at the top of the conversation wheel tend to lend themselves more towards the Paragon (Light side) play style. Sentences at the bottom of the wheel will more often than not result in Renegade (Dark side) points. Then you have dialogue options that become available only when you've spent points in either the Charm or Intimidate talents. Charm dialogue options appear in blue, and will result in Paragon points; Intimidate options appear in red and will get you Renegade points. Add to this choices that allow you to investigate further or options that move the conversation towards a swift conclusion and what you have is a simple yet dynamic system that never grates. It's great fun to just pick an option that you just know will end up getting whoever you're talking to really pissed off - if you're playing as a Renegade that is.

One of the most thrilling bits of Mass Effect is where you deliver a morale boosting speech to the crew of the Normandy. You get to shape the speech, choosing whether to inspire with warm words of encouragement or demanding threats, all to a suitably heroic score. It's a superb highlight and something that will probably stick with me for years to come.

Of course, video games have been allowing us to decide between right and wrong for years now. Indeed the KotOR games provided clear indications of what would earn you Light side points and what would earn you Dark side points. The moral decision-making in Mass Effect is not a revolution by any stretch of the imagination, and nor does it blur the lines between right and wrong, but it does force you to make some tough decisions and allows you to shape the story more effectively than anything we've seen before. A case in point - the game forces you to decide who should live out of two of your compatriots - characters you've spent a great deal of time levelling up and developing an emotional bond to. Most missions will allow you to shape the way in which you tackle them - either subtly with the least amount of death or gung-ho with no care for casualties. Most boss encounters will let you decide what to do with them once you've forced them into submission - whether it is murdering them in cold blood or setting them free, the choice is yours.

Don't mess with Wrex , he'll bite your head off.

And there's a real sense that your decision making has an effect on the Mass Effect world and the people who live in it. In fact, one of the first things you need to decide upon if you dump the default Commander Shepard and create your own character is your early history (Earthborn, Colonist or Spacer) and your psychological profile (Ruthless, War Hero or Sole Survivor). These decisions will affect how the game's characters react to you. One mission presents an opportunity to kill off an alien race for good. If you do, your Codex, an evolving historical record of the galaxy, will mark that species as extinct. In another situation, a journalist asks you for a few comments on your mission to save the universe. Storm off in a childish huff and later in the game you'll be informed of how public opinion is turning against you back on Earth, and how a PR machine has been put in motion to smooth things over. And there are of course a few different love sub-plots which you can pursue. The decisions you make as either a male or a female Commander Shepard will either hinder or help your efforts to get your object of desire into bed (yes, there's nudity in Mass Effect boys). It's little things like that which give you a sense that deliberating over tough decisions is more than a consideration over Paragon or Renegade points.

Mass Effect is still an RPG at heart of course - the Gears of War style combat cannot detract from that. Just like in KotOR, you'll find that much of your time is spent running around planets, space installations and the Normandy, talking to NPCs, getting side quests, running errands and generally letting yourself tumble into the game's world like Alice down the rabbit hole. The side quests are probably the game's weakest in terms of refining the KotOR mechanic. Most will involve an NPC in distress, for example an alien who wants you to help him develop his betting outcome device by attaching it to high stakes gambling machines, or a human security guard who wants you to get rid of a preaching alien. In almost every case you're presented with a moral decision - so you can decide to turn the betting device in to the authorities or help him out. Or you can convince the religious alien to give up and rethink its life or find him a preaching permit. Most will follow this pattern. Collect side quest, resolve it in whatever way you see fit, collect the credits and experience points and move on.

If the side quests stand out as a tad disappointing, it's only because of the quality of the overall experience. It is a sci-fi fan's wet dream, with movie quality presentation, storyline and score that's a real showcase for the 360. Mass Effect is the game every Blade Runner fan has been anticipating for years, and BioWare has done a stupendous job of creating a world that is not only engaging but completely drenched from head to toe in futuristic cool. You feel it everywhere. It's in the tremendously effective film grain effect which is washed over everything, giving proceedings a more cinematic feel. It's in the wonderful 80's sci-fi inspired score, a soundtrack surely destined for separate release. It's in the impressively detailed cut-scenes, whether it be landing the Mako rover on a far away planet or a full scale galactic conflict overlooking an embattled space station. It's in the game's physics, which sends enemies spiralling off ledges and slowly floating away in zero gravity environments like rag-dolls on speed. It's in the plot, a superb tale full of political machinations, mysterious alien races, hidden artefacts, shocking revelations and an evil alien commando gone rogue. It's in Urdnot Wrex, the tough talking and reclusive Krogan Battlemaster who joins you on your quest. It's in the game's sound effects - the pulse of the sniper rifle, the ripple of space as you invoke a Singularity, the gravitas of simply bringing up your squad's power wheel. And it's in the Elkor, an alien race so depressing and yet loveable that you'd throw Winnie the Pooh's Eeyore and Yogi Bear into a river if it meant you could take one home.

Mass Effect is not without its flaws - what game isn't? Riding around in the Mako rover, the APC/dune buggy hybrid with a cannon, isn't half as much fun as it ought to be. The driving sections are often drawn out and at worst boring - something I'm sure BioWare will be thinking about as it works on the game's second instalment. As I've said, some of the game's side quests could do with a bit of work. One optional quest which sees you investigate rogue AI on the Moon is a monotonous affair involving repeating the same mass destruction of robots in three identical buildings. Problem is, it's pretty much essential, since completing it allows you to specialise from within your class. Equipment can be extremely annoying. The game would have benefited no end from an optimise option, allowing you to quickly and easily kit your squads out in the best possible gear from the giant dustbin that is your inventory. As it is, whenever you loot something of value you have to manually go through everyone's equippable slots, one for each weapon, for armour, biotics, grenades etc, and work out if it's better than what you're using. It makes for often long breaks in play that disrupt the flow of combat and exploration. Then two seconds later you open a crate, find something that might be even better and have to do it all over again. Optimisation could have been completely optional of course, so stat whores could pour over bonus modifiers in minute detail (this is an RPG remember), but it would have helped avoid the ridiculous situation of having to convert every new item you pick up into omni-gel whenever you reach the 150 item limit. You can't even switch back to your inventory to dump some old equipment when this happens - you have no choice but to get rid of the new stuff, good or bad.

The evil android Geth are out to stop you at every turn.

The game world is perhaps a tad small for your veteran RPG gamer. When you get access to the Galaxy Map for the first time the game can seem gargantuan. You soon realise, however, that you can't land on most of the planets. This isn't to say the game is short - I left out about a third of the game's side quests and it took me just over 20 hours to complete. Some might say that's short for an RPG. For me though, it feels just right for a first play through. But the best thing is I feel compelled to play Mass Effect again, something I rarely get from games these days. I'm going to play as a different class, as a different gender and with a different play style. The fact that there's also the option to start again with the same character at the level you finished the first play through on, and with all your high-end gear and weapons, makes compulsion to replay even greater.

While Mass Effect's graphics really are a sight to behold, and the later levels provide some of the most impressive environments the 360 has ever seen, they also cause a few problems. There are moments of Halo 2 syndrome, where character armour and environment textures take an age to load. The game can jerk a bit too, and suffers from regular tearing. And we're not sure about characters' eyes - especially Commander Anderson's. There was more than one occasion where eyes seemed to be pointing in random directions or looking like they were mimicking WWE Superstar The Undertaker. Perhaps the game suffers from having to be completely accessed from the game DVD - Mass Effect makes a lot of noise in the disc drive.

These are mere niggles, and while you shouldn't ignore them you certainly shouldn't be put off by them. Despite BioWare's efforts to disguise the game's roots it's still an RPG and will mostly appeal to male hardcore gamers (a lack of an in-game tutorial is evidence of that). It's not an attempt to revolutionise gaming as we know it. But that's no bad thing. Mass Effect is a triumph. A triumph for the science fiction video game, a triumph for the action RPG and a triumph for next generation gaming. And it sets up the sequel perfectly. I want to know what happens next. I want BioWare to release new planets as DLC. I want online co-op so other people can take control of my squad members. I have had a sip of this bewitching cocktail and now I want to down the whole lot. Bar a pre-Christmas release of stupendous proportions, Mass Effect is my game of the year.