Most platformers are won or lost by memorisation. Learn the controls and study your terrain and you'll eventually end up on top of the flagpole or through the spinning golden ring. In Spelunky's procedurally generated world, however, the comforting familiarity of muscle memory is nowhere to be found - the fun, if you will, comes from conquering the unknown.

Yet despite this inherent randomness, Spelunky's world is one of mechanical precision. The game's monsters, traps and chasms run like clockwork, and for the most part the two-strong development team at Mossmouth have ensured that manoeuvring the game's multiple floors is both intricately engineered and neatly balanced. Occasionally, however, the random level generator feels decidedly unfair - and some rare decisions (like shrouding the level in complete darkness) add far more frustration than they do challenge.

Spelunky's goal is simple: you start at the top of a cave, and must spelunk your way down its various floors. The challenge is in the journey, for life is fleeting in Spelunky and death is permanent. It's also frequent: I've been punctured on spikes, bitten by spiders, chomped by piranhas, eaten by a plant and (but only once) bashed open by a yeti. I've never gotten that far in the game again. I certainly haven't completed it, that's for sure. I haven't even seen the fourth and final area.

Despite the cavernous setting, the game isn't actually that deep - you could probably make it from top to bottom in ten minutes if you never let go of the run button and had the hand-to-eye coordination of a superhero. I'm not nearly that talented, however, and even after playing it for yonks I still feel like I'm just a bit crap. But that's Spelunky in a nutshell - it's a game that will make you feel a bit crap.

Sometimes, but certainly not always, it will make you feel crap in a good way and everything becomes very exciting. Maybe you'll be making good progress on a speed run or a high score, and you'll start to feel like your adorable little adventurer has been somehow mystically enchanted with a fortuitous run of luck, and then you'll land on some spikes and die.

Spelunky might be brief, then, but it's absolutely packed with content. Its simplistic premise masks the sheer variety of things you'll end up uncovering, mostly by accident over the course of hundreds of plays. While the end result of most discoveries will be the same - a sharp, fatal death - it can be a real pleasure to slowly unravel the full breadth of the game over time. It's in these discoveries, often recorded into your in-game journal, that will spur most players into repeated playthroughs.

Actually improving at Spelunky requires both patience and precision, then, and a mind that can work through a mental laundry list of each potential problem and pitfall. You need to remain constantly aware of your surroundings every single time you play, though the game gently goads you into high-risk situations for the maximum reward, and you'll only have yourself to blame when a vendor greets your attempt at shoplifting with a shotgun blast, or a boulder grinds you into a fine paste. Thinking about it, Spelunky is probably the dream game for anyone who works in risk assessment.

This jazzed up XBLA version, a reworking of the original freeware PC title with a particularly lovely new art style, also contains well-intentioned support for local four-player co-op and deathmatch modes. While perfunctory in the short-term these don't quite hold up to sustained play, making the game far too hectic and throwing off the delicate sense of pace and balance that helps the single-player mode straddle the line between entertainment and agony.

This is a game of strict and deflating challenges, then, and while Spelunky is a fine addition to the growing library of masochistic titles it doesn't always quite manage to elicit the right response from its players. There are occasional moments of intense euphoria to be found here, but all too often Spelunky just makes you feel crap.