Assassin's Creed was a massive commercial success, yet it received the most mixed reviews of any high profile release in recent memory. Under the circumstances, developer Ubisoft must have questioned what really needed changing for this sequel. For every critic there was someone willing to shoot down the naysayer. For everyone who claimed the free-running was awkward, there was an angry fan keen to get their point across. Yet looked at from a neutral point of view, the first, clearly ambitious game had some glaring faults that had to be ironed out for this hugely anticipated follow-up. The original laid down the groundwork, but the sequel had to patch over the rough spots and fill in the missing pieces. Assassin's Creed 2 hasn't re-written the free-roaming action assassination rulebook, but it has refined the gameplay to create an altogether more enjoyable and diverse experience.

Plenty of spoilers for the first game follow, so be warned if you haven't finished it yet. Assassin's Creed 2 picks up immediately after the bizarre 'Desmond staring at a wall of glyphs' ending of the original, with the hoody-wearing bartender once again trapped inside a lab at Abstergo Industries - a company which just so happens to be run by a modern day version of the Knights Templar. These guys used a device called the Animus to make Desmond recall ancestral memories - in the original game, the memories of Altair, a member of the Assassin Clan during 1191. Altair and the other assassins were trying to find the Piece of Eden, an artefact able to create illusions. This is exactly what the shady Abstergo is after, and the reason they kidnapped Desmond.

It's complicated stuff, and the plot gets even more hard on the brain during the events of this sequel, in which Abstergo employee Lucy Stillman helps Desmond out of the complex and into a secret facility that has its own Animus device - dubbed the Animus 2.0. This time Desmond is recalling the memories of Ezio Auditore da Firenze, a young Italian man who seeks revenge on the men who betrayed him and his family in 1476, almost 300 years after the events of the first game. Ezio begins the game as a stereotypical suave young man, but tragic events and the discovery of his family history send him down the path of his forebears, as he becomes a deadly, cloaked assassin.

As in the 2007 game, Assassin's Creed 2 takes place in numerous open cities, with large swathes of countryside to explore in-between. Being set in Italy, you've obviously got brand new locations to visit, including Venice (complete with row-able boats), Florence, Romagna and Tuscany. Each is stunningly reproduced here, with even more attention to detail than in the still beautiful original. Hundreds of civilians go about their business, guards patrol the streets and roof tops, and, more importantly, each place is packed with things to do. There is a core series of storyline missions to play through, but these only represent a portion of what's on offer. Ezio is even more nimble than Altair, so he's more than up to the job of climbing the numerous towering buildings scattered about each city. Reaching the top of marked 'viewpoints' will reveal a hidden part of the map, simultaneously unlocking new missions.

The double hidden blade kill. Nice.

One of the many complaints levelled at the first game was that you often felt like you were doing the same things over and over again. As Altair you'd go to the Assassins Bureau in order to get some tips on where to look for clues about your next target; you'd then head off into that area, draw information onto your in-game map by scaling numerous view points, and then complete the required number of investigation quests before you could finally attempt the assassination. These investigations were, let's be honest, not that great, and it's no surprise to find that entire system is missing in Assassin's Creed 2. The best of these tasks (beating people up, courier missions) and some new ones (races and one-off assassinations) have been turned into completely optional side missions for the sequel, rewarding you with cash if you complete them. The core story missions are free to play whenever you like, and you feel less shackled as a result. You'll still be building up to key assassinations, but the lead up missions are far more entertaining and varied than before, and the sense that you're working towards your goal is greater.

Outside of this core change to the way the game is structured, the various gameplay mechanics of the original have been refined, completely rebuilt or added to. Blending, which lets you take cover within a group of people while on the move, has been reworked so that you can do so within any small group of people - wander up close to them and you're effectively hidden from guards. Various groups offer you their services for a price, and these people distract guards or give you fully controllable mobile cover. But unless you pay for this help, you have to hop from group to group if you want to remain 'blended', as they rarely walk where you want them to. If a line of guards is stood blocking an entrance that you must use, and you can't find another way in, you can pay a group of thieves to rob them and run off. The guards won't stand for this, and leave their posts to chase after the criminals. This opens up the entrance so you can wander right in.

Doing naughty things, like pickpocketing (no longer a mission type, simply done while wandering about behind people), clambering about on rooftops or killing someone, will get you noticed. Do enough bad things and your notoriety will max out, and the guards will come after you if you're spotted. You can evade the chasing pack by outrunning them and finding a hiding spot (although guards will look more thoroughly than in the last game), but your notoriety will remain on red alert. This can only be reduced by carrying out tasks to lower it, such as bribing public speakers, killing officials and ripping down wanted posters. It's a neat system that is more realistic than guards just forgetting about you, and it has been handled in a way that makes the process fun and fairly simple.

Ezio's story is epic

Running might not sound like a terribly thrilling thing to do in a video game, but few games make it as fun as it is in Assassin's Creed 2. The Parkour-inspired system of the original is back, meaning Ezio can leap across rooftops, skip across beams and clamber up walls, and all you need to do is point him in the right direction. It's initially easy to get carried away and run full pelt at all times. Doing this is a recipe for disaster, though, as Ezio has no regard for his own safety when you've got the sprint button held down. Reach a sheer drop and he'll gladly leap off, more than likely to his death. It pays to hold back on top-speed manoeuvring until you know you want to leap across a gap, as medium speed Ezio will prevent himself from blindly jumping off into oblivion. Once you've got this mastered, running about the cities is incredible fun and one of the game's defining features - something Ubisoft should be very proud of.

When you do get into a fight, and it'll happen often, the counter-based melee combat of the original game returns - and it's just as satisfying as before. It won't be for everyone, and certainly lacks some of the depth found in the recent Batman: Arkham Asylum, but you'll need to use different techniques on the more advanced guards, make use of your new disarm ability, and use the various new weapons hidden under your outfit - dual hidden blades are always a thrill to use. Inventor Leonardo da Vinci becomes a friend early on, and he puts his skills to creating new tools and gizmos for Ezio - including the brilliant flying machine that Ubisoft showed off at E3 earlier in the year. The combat here is improved over the first title, yet still accessible for gamers who aren't experts with combos and hugely difficult timing. There are more weapons, new items (the smoke bombs are brilliant if you're in a tight spot), and a brand new damage system - repairs must be carried out on your weapons and armour by visiting blacksmiths.

Assassin's Creed 2 is a massive game. Even if you skip the vast majority of the secondary missions you're looking at roughly 20 hours of gameplay. But you'll want to spend more time in the world because you're rewarded for collecting hidden items. The flags seen in the first game have been replaced by feathers (100 of them), there are 330 treasures to collect and, best of all, Prince of Persia-style catacombs to find and explore. These Assassin tombs feature some of the most challenging platforming gameplay the game has to offer, yet once you've completed the first the rest are completely optional. The reward for finishing them is worth it though, especially for fans of the previous game's hero, Altair.

Your uncle's villa is located in the run-down town of Monteriggioni, a settlement you can rejuvenate with refurbished buildings and by using the various shops and services. Do so and you'll earn money from the increased business traffic, giving you a steady income to use on repairs, new tools, health services and the frequent need to bribe people. If you want to, you can spend an obscene amount of money collecting art. It's never forced on you, but it's something certain players could spend hours doing. The same is true for the glyphs drawn on buildings in the cities: Decipher them by completing puzzles and you'll unlock what the game calls 'The Truth', but ignore them and you'll be able to carry on with the game regardless. This is one of Assassin's Creed 2's biggest strengths. While the main storyline is predominantly linear, everyone will play through the game in a different way, and never will you feel like you're being forced to carry out repeated tasks.

Each of the locations has been stunningly recreated

This complicated, hugely ambitious game is wrapped up quite gloriously by some of the best presentation seen on the current generation of systems. The cities are the stars, modelled with such attention to detail that you could lose hours sightseeing, but Ezio and the other key characters are equally impressive. If there's a slight blip it comes from the occasional odd-looking animation, and a bit of frame rate trouble here and there (more prevalent, along with screen tearing, in the PS3 version) and plenty of pop-in, but you can't help but be impressed by what Ubisoft has created here. Voice acting is top quality, too, with the assembled cast all putting in believable performances that run the gambit from emotional to downright funny. The game world feels alive and adds an immeasurable amount to the experience as a whole.

Coming out so close to Call of Duty: Modern Warfare 2 was risky for a number of reasons. MW2 is a quality product, so any weaknesses in games released so soon after would stick out like a sore thumb, and critical responses could have had a negative impact on sales. With the original game coming up short in a few key areas, any slips by Ubisoft would have been flagged up for all to see. Almost all of these causes for concern have been addressed, either reworked or replaced by something better. The storyline is intricate, there's depth beyond the main quest, the presentation is wonderful, and the action is incredible at times. We've had some stunning single-player experiences this year, and Ubisoft has given us another gem to add to the list.