You'd be forgiven for thinking Spelunky an unambitious and derivative platformer at first glance. The unassuming art style and simple controls do little to differentiate it from numerous other indie attempts, many of which have been floundering in Microsoft's Indie Games store for years now. But the simple presentation and gameplay belie one of the most complex, challenging, and at times downright infuriating games to grace Xbox Live Arcade in a long time.

The premise of Spelunky is simple. You will take control of one of many spelunkers looking to probe the depths of an ancient mine shaft long since abandoned to nature. Although a traditional sidescroller in many respects, Spelunky also borrows heavily from the rougelike genre, and this is where things get truly interesting. Each time you delve into the mine, you will begin with four hit points, three bombs, and three ropes. The ropes will allow you to climb up to otherwise unreachable heights or descend cliffs otherwise too steep to tackle, while the bombs will allow you to blow up the walls of the mine and create new paths. Your most valuable resource by far is your hit points, though, as in traditional rougelike style your character will permanently die once all of his hit points are depleted. Once dead, any items you may have hoarded up to this point will go along with you.

To make matters worse, the mine is littered with enemies and devious traps. Snakes, spiders, scorpions, and worse will litter the mines, and must be dispatched with your trusty whip. Each enemy type will have its own behaviors and tendencies, so learning how the enemies behave becomes just as important as learning how to kill them off. While it's certainly possible to fall prey to the numerous enemies and their distinctive attack patterns, the traps will most often be your undoing. Spikes litter the floor of many a mine shaft, and touching them means instant death. Worse are the arrow blocks, which respond to any movement with a quick and damaging arrow blast. As you spend more and more time with the game, you will discover many ways to cleverly circumvent these traps, all without any prompting from the game. Spelunky is a game that trusts players to assess the situation at hand and overcome it without holding their hands through the process, and this makes overcoming some of the tougher challenges all the more satisfying.

Tough is almost too nice a word for some of the challenges that the game throws your way. Each area of the mines is randomly generated from a series of preset tiles, so although you may recognize a tile or two from an earlier playthrough, the individual levels should never be the same twice. This can result in some truly despicable levels teeming with spitting cobras, spike traps, and all manner of nasty surprises. But the random design of the game is also the most compelling reason to keep coming back. Even though you'll be dying all the time, re-exploring the mines never feels like a chore because each level is unique.

Items in each level are also randomly generated and placed, giving the game some of the addictive edge of something like Diablo. Although you'll never find yourself looking at a character sheet wondering whether to equip this pair of boots or that, you will stumble upon many items that, when collected, bestow unique powers upon you, or vendors hocking their wares deep in the mine. Collecting the cape, for example, will allow you to glide over large gaps, while the compass will always point you to the exit of the cave and the entrance to the next section of the level. There is a ton of this kind of loot in the game, and while all of the items are (sometimes critically) useful, you will often be asked to weigh the pros and cons of each, as when a vendor appears in a mine his items are often too expensive to purchase all at once.

That brief synopsis barely even scratches the surface of the depth at play in Spelunky. I could go on for pages about secret items, hidden altars with sinister effects, idols that call down all-destroying boulders, and much, much more, but at times it's best to discover the wicked joys of the game for yourself, and I would be remiss to spoil much of the surprise. The fact is that there is so much content jam-packed into this inconspicuous little package that you could easily spend days exploring the depths of the mines without seeing it all. And when you finally do escape the grasp of the mines, other, even more challenging worlds await.

With so many variables coming into play each time you start up a level, a game of Spelunky quickly becomes a meticulous exercise in self control. You will have to carefully examine your environment for enemies and traps, decide whether that blocked-off treasure chest is worth using one of your precious bombs to reach, and control your gold hoarding urges in the name of pure, simple survival. It's not always easy. In fact, sometimes it's infuriatingly difficult. It's important to make a distinction between difficult and unfair, though, as if Spelunky is anything, it's fair. Everything in the world operates under the same set of rules, meaning that what kills you also kills your enemies. Push a scorpion into a spike pit, and it will die just like you would. This fairness keeps the game from becoming overwhelmingly upsetting, even when you die on the last few levels and have to begin your meticulous dungeon crawl all over again.

Spelunky also boasts splitscreen multiplayer. If the single player adventure is a careful crawl through dangerous traps and foes, the multiplayer is the exact polar opposite. The dark cloud of permadeath still hangs over each game, but the game has also built in a few irresistable possibilities for griefing your buddies that makes it a much more lighthearted affair. While up to four players can participate in a game, only one of them, marked with a white flag, controls where the camera moves. Because of this, that one player has a sort of power over all of the others. He can run to a completely different section of the cave and leave everyone else fighting blind. The inverse of this is that dead players come back as ghosts who can manipulate objects in the environment by blowing them through the air. Friend just griefed you and left you to die? Get revenge by planting yourself by the exit and blowing him back every time he tries to exit the level, or toss all manner of enemies and items his way with your powers. Ghosts can also do sick flips with a tap of the A button, which doesn't seem to have any effect on anything, but hey, SICK FLIPS!

While the multiplayer adventure mode seems to turn into a sort of sick deathmatch more often than not, there's also a proper deathmatch mode available outside of the adventure. This mode plops up to four players into a small arena littered with the occasional item for good measure. Of all the ways to play Spelunky, deathmatch is easily the most poorly thought-out. Victory often goes to whoever tosses out the first bomb, as being hit with one of the projectiles initiates a stun period that conveniently lasts exactly as long as the bomb's fuse does. Other items, such as a laser blaster, give whoever grabs them an almost insurmountable advantage. As a result, games of deathmatch are highly chaotic and even fun at times, but also highly unbalanced and unweildy. In a game that is otherwise so carefully crafted, it sticks out like a sore thumb.

Spelunky is at times an infuriating challenge. The combination of randomly-generated levels and permadeath can make it hard to want to get up after being knocked down by one of the game's many devious traps and enemies. But get up you will. The drive to play on, to discover that next piece of loot or that next section of the mines, is just too great, and that drive is what elevates the game beyond your average platformer and into the realm of pure, masochistic bliss.

Score: 9/10