Aside from the benefit of "letting off some steam", most psychologists would likely infer that spending endless hours killing in the virtual world is perhaps not the healthiest of recreational activities. Still, killing is what we want and publishers are all to happy to fulfil the public's blood-lust; whether we're sniping Nazis with antique rifles, setting zombies on fire, blasting UFOs out of the sky, or hacking dozens, nay hundreds, of hapless soldiers to pieces with a sharper-than-it-looks Chinese fan, the art of murder has become a comfortable fixture in the majority of action games.

Thus explaining the appeal of LocoRoco to the blood-thirsty masses is something of a challenge. A game that contains no guns, gore or garrotting, it instead places you in a bright, candy-coated 2D platforming world where the sum total of your task amounts to bouncing the LocoRoco - essentially a big blob with a cute face - to the end of each level. Plot is largely non-existent but the basic idea goes that LocoRoco's live on a peaceful planet, looking after nature, and singing hyperactive melodies everyday like life is some kind of 24-hour caffeinated disco. Or something. However one day, they come under the attack from the Moja Troop; jet-black, flying bundles of scum with creepy dreadlocks (or perhaps they were tentacles, hard to be sure). Defenceless, the blobs must rescue their scholarly (read: cowardly) friends, the MuiMui, who are in hiding throughout the levels, and liberate each area from the Moja.

The clever bit comes in the control scheme. Rather unusually, you assume the role of the planet, and so instead of navigating your LocoRoco with the directional buttons, movement is attained by tilting the environment one way or the other with the L and R shoulder buttons; causing the blob to roll in the desired direction, whilst pressing them together causes it to jump (or perhaps 'bounce' is a more accurate description). Pressing 'circle' causes a lightning bolt to split your LocoRoco into several small ones, allowing you to slip through tight gaps in the scenery, while holding the same button causes them to reform. It's as simple as that.

The gameplay is finely judged. Never dull, but serene enough that you never feel you're being rushed; everything in this weird wonderland feels just right. An almost hypnotic gaming experience, it's reduced myself and many individuals I have known to a state of gentle swaying, inane grinning and general chewing-gum-for-the-eyes happiness. The crazily infectious soundtrack deserves much of the credit for this; it's hilarious to watch the blobs appearing to mime along with the lyrics, even when some have been unceremoniously bounced upside down. It's all the more impressive considering that designer Tsutomu Kouno penned the lyrics in a fictitious language, derived from Japanese, so the unusual style can baffle all in equal measure.

As well as some fabulously upbeat and alliterative J-Pop numbers, Kouno flirts with a host of other musical styles, and in doing so ensures that each LocoRoco you unlock is distinctive thanks to their music and voicing. The child-like Yellow you begin the game with is followed by Pink - who has a softer, French-accented female voice and sings some quite soulful numbers. Blue, Green and the rest that follow appear to flit between jazz, latin and calypso. The difference in gameplay terms is purely cosmetic, but the variance in their songs and voices (they alert you if a Moja is near for example) means its fun to switch now and then even if you have a particular favourite.

Many of the game's most pleasing moments are centred around smart level design, which plays to the games aesthetic qualities. Just as the early Sonic The Hedgehog titles were devised in a way that would accentuate its lightning-fast speed, LocoRoco raises smiles when the jelly-like creatures get on the end of the games various visual effects. They can be chewed up by random owls and spat out in a different shape, or split into fifteen and sent hurtling through the sky via a vacuum, or indeed when a bunch of them follow each other one-by-one through the cogs of turning gears or bobbing through water.

The aims of each level includes finding red berries which, when consumed, grow your LocoRoco - you start with just one, and can expand to the size of twenty in any single level. Along the way you'll have to avoid spikes that can injure and thus shrink your blob, and likewise those evil Mojas will swoop in and try to take a bite out you. There are moving platforms, air fountains, spring pads and various other devices that require you to master the tilting controls, as well as the odd change of surface which leads to some unusual physics. Wintry levels offer very little traction and generally hurtle you around at high-speed, whilst the soft ground is slower to move through as the LocoRoco sinks in to it. There is even the occasional puzzle, such as splitting the LocoRoco's so they can separately press down on three switches simultaneously; it's a shame their weren't a few more teasers like this, though there's plenty of platforming to keep you happy.

How much you put in dictates how much you get back, though the game will feel equally enjoyable for novices and seasoned gamers alike. Newcomers are just as likely to finish the game - bopping through the levels and seeing the sights doesn't make for any less engaging an experience, as you'll still get to witness all the clever bits and colourful scenarios. For those willing to deliver a little deeper, there's plenty of secrets hidden away in each level. Once you've developed an eagle-eye, you'll spot pieces of wall that are slightly the wrong shape, allowing you to jump straight through and discover a secret area. Similarly, suspiciously-flat bits of 'roof' are worth bouncing into as they can be smashed to reveal new areas.

The net gain of all of this is reflected in the LocoRoco House. Essentially a feature to play around with, rescuing MuiMui's from the levels grants new music, larger house models and literally dozens of different building blocks, giving it the feel of a mini-level editor. Admittedly, compared to the main game, the House will get relatively limited use, though there's also a trio of mini-games, the best being an arcade-style, UFO-grabber game.

On top of its other qualities, it's also among the most beautiful games ever released for the PSP. The simplistic utopian world is quite childlike, yet wonderfully vivacious; its uncluttered yet attractive levels use bright shades and hues to gorgeous effect. It's sharp and high-resolution, resulting in some eye-poppingly vibrant menus, whilst in-game LocoRoco repeatedly impresses with flawless-looking characters that merge perfectly with the environments, which themselves are populated with beautiful little details that make the world feel more active.

...And 40 levels is plenty to seek your teeth into. It may be argued that over the distance, the game's simplicity starts to work against it a little as maintaining a tangible sense of variety becomes difficult. That said, it's hardly a one-trick-pony and is an ideal game to play on the move in twenty minute bursts. Playing a couple of levels a time ensures you never get frustrated but still get the mind working.

LocoRoco is not only a victory for originality and oddness; it's a great success from a design point of view and a lot of fun to play. As a 2D platformer it's unique, and a great fillet for the PSP, which has been criticised for not having enough in the way of defining exclusives. A quirky ray of sunshine, it may prove just the tonic if you've become jaded from all the killing.