How do you improve upon one of the greatest games of all time? It's a question Nintendo has answered countless times before, in The Legend of Zelda series, the Metroid series, and, of course, the Super Mario series. Now, with Super Mario Galaxy 2, it's trying to do it again.

Some have criticised Galaxy 2 for looking like little more than Galaxy 1.5. What tosh. If Mario Galaxy 2 is brilliant - and our extensive hands-on with the game at Nintendo's European Gamers Summit last week suggests it will be - what's the harm? This ill feeling probably has something to do with Nintendo's release strategy - it rarely releases numerical sequels. When we do get a new 3D Mario game, it's usually a new concept: Super Mario 64 to Super Mario Sunshine to Super Mario Galaxy. Now, for the first time, we have two main 3D Mario games on the same console: the Nintendo Wii. Some have deemed this a bad thing, as if somehow Galaxy 2's mere existence is preventing Nintendo from developing the next evolution in the Mario series. To this we say: nonsense.

At first glance, however, you'd be forgiven for leaning towards the naysayers' argument. Galaxy 2 looks a lot like Galaxy. It has the same vibrant, colourful art style and many of the same, planet to planet mechanics. The camera often switches perspective, ranging from following Mario as he walks around the surface of a planet, to old-school side scrolling, via more open plan platforming. The controls are also the same. Basic jumping and running is punctuated by shakes of the Wii Remote to spin. It's simple, accessible, and as responsive as ever.

So, what's new? The answer comes in the form of a little green dinosaur with a long red tongue, namely: Yoshi. That's right. Yoshi, Mario's long-standing companion, is in Mario Galaxy 2, and his presence has made for some interesting new gameplay mechanics. As is his way, Yoshi eats everything. By pointing the Wii Remote at an object, a small circle quickly fills red. Once done, Yoshi can extend his tongue, use it as a swing, pull levers, swallow enemies, or, more interestingly, gain power-ups.

Yoshi is the big new addition, but he's not all that's new.

For example, the Blimp Berry turns Yoshi blue and inflates his stomach, sending him floating up and away as he exhales air. But the air only lasts so long. When it runs out, Yoshi and Mario will fall back down to earth. Luckily, if he eats or touches another Blimp Berry, his lungs will fill with air again and the countdown timer will be reset. In one level we played, the camera switched to a side-on perspective, challenging the player to float in and out of platforms to gain coins, avoiding enemies and grabbing fresh Blimp Berries in order to reach the end of level star.

The Dash Pepper gives Yoshi a temporary speed boost, allowing the player to run up steep hills. If Yoshi and Mario are still standing on a steep hill when the Pepper runs its course, then they'll slide down. In another level, Bullet Bills fire from all directions. If Yoshi eats one, he can spit it out as if firing his own Bullet Bill - aimed by pointing your Wii Remote - defeating enemies, destroying mines, and smashing bits of the environment, like glass walls. These are only a few of the power-ups Yoshi can gain as a result of eating objects within the game world. Nintendo promises many more.

Yoshi isn't the only recipient of new toys; Mario's got some new tricks up his sleeve, too. The Drill Bit, activated with a shake of the Wii Remote, allows Mario to literally drill through a planet, going through the core and out the opposite side. You can only use the Drill Bit on certain planets, and only then when the earth itself is of a particular type, but it's worth the wait. Perhaps out favourite moment during our hands-on occurred when battling an end boss designed to challenge our Drill Bit skills. The mechanised monstrosity with spider-like legs could only be defeated by drilling through the planet and emerging at the other end underneath the boss, hitting its vulnerable underbelly. It was pure, unadulterated, joy, and classic Nintendo.

Again, Nintendo proves the Wii is capable of great things.

Galaxy 2's power-ups make for a different game in the same way that new toys make an old play area instantly more appealing. But Nintendo knows power-ups alone won't satiate the Nintendo hardcore's sense of abandonment. That's why Super Mario Galaxy 2 may well be the hardest 3D Mario game ever made.

Really, some of it is brutally hard. At the end of Bowser Jr.'s Fiery Flotilla level, Mario faces off against a huge snake-like dragon that stalks the Italian plumber as he runs around a small planet. The idea is to run for your life, praying that when the huge dragon decides to bury its head into the planet and tear through the core and out the other side, it doesn't hit you. If you manage to stay on your feet, you then need to stand next to its body and spin attack just as the pink parts of its body speed past. It's pretty hard. Nintendo wasn't joking, after all.

That level, though, is like one of those horribly simple mini-games the Wii's flooded with in comparison to the Flip-Swap Galaxy level. Here, the platforms on which Mario stands are panels. The idea is to flick the Wii Remote mid-jump to switch the position of the panel he just jumped from, to a position that, hopefully, will give him something to land on. Not only do you have to contend with jumping, flicking the Wii Remote (which doesn't always result in a panel switch - wouldn't it have been better assigned to a button?), and working out when and where to land, but you have to collect all of the purple coins in the level to complete it. And you have only four minutes in which to do it. It's devilishly difficult, challenging hand-eye coordination in ways we thought gaming had forgotten. It's great, but expect to die. A lot.

Setting what's new about Galaxy 2 down like this, it doesn't sound like much is different, does it? So why are we so enthusiastic about the game's release? Because it's going to be brilliant. How do we know this? Well, we just know. This seems like a woefully unscientific analysis of the game, but in many ways, it's the only way to make sense of Nintendo's Mario magic. Often, when we critique video games, we discuss their constituent parts in isolation. We judge the visuals, audio, mechanics, level design, and features, and then determine an overall score. But really, video games are more than the sum of their parts. They're an experience. They're entertainment. They're fun.

Did we say Mario Galaxy 2 is brilliant?

Mario Galaxy 2, like all Mario games before it, is the epitome of this design philosophy. Its levels are memorable; its art style is vibrant and colourful; and its mechanics are as easy to pick up and play as they are fun to use. But the game's appeal is about more than mere snippets of praise. Mario Galaxy 2, like its predecessor, has that special something, that je ne sais quoi, that Nintendo magic - that's so hard to define - in spades. There were more than a few moments when we actually said out load, "wow", and it wasn't because we were witnessing groundbreaking graphics, brutal combat, or vistas that extend farther than the eye can see. It was because Nintendo knows how to do pure gaming fun better than anyone else.

Basic mechanics challenge you in ways you can only describe as genius. The Drill Bit's the best example: it's a simple, almost obvious, power-up, but you use it in ways you'll never forget. How do you improve upon one of the greatest games of all time? You focus on doing what you do best. Sometimes, that's all you need.

Super Mario Galaxy 2 is due out in Europe on June 11.