This game has actually been available for free on PC for some time and is something of a fan favourite, but developer, Mossmouth, decided to not only go back and re-release it across consoles, they updated the game to fit the modern gaming world.
None of that really matters though, because it's an indie-developed game and you should buy it just to support them anyway. Spelunky is a challenging platformer that breaks all traditional platformer rules by upping the challenge thanks to procedural level-design (read: no memorising power-ups here) and a do-or-die start-over system. James Cottee ran it through its paces for us.
Click here for his full thoughts.