Sometimes a video game is like a razor blade. Only millimeters thick, yet sharpened to a fine edge sharp enough to draw blood if you're not paying attention. Once you learn that truth, such a game requires your total attention lest you wind up bleeding a lot. Spelunky comes to the Xbox 360, sharp enough to etch itself into your memory, time and time again. And even though you'll wind up raw from its rough scrapings of your mind and reflexes, you won't be able to stop playing.