Let's say it like it is: without Halo, it's likely the Xbox would've gone the way of the Saturn. Bungie's epic sci-fi shooter defined the term "killer app" and invented a new one -- "Halo Killer" -- by presenting a game that did nearly everything right, from performance to story to Martin O'Donnell's masterful score. The Master Chief's war against alien zealotry earned him iconic status right out of the box, and the unnerving mid-game introduction of the Flood remains one of the greatest twists in gaming history.

Was it perfect? No, as anyone who's experienced the Library can attest, but good luck finding a console shooter that doesn't liberally borrow from the Chief's example. His was a tight, intuitive control scheme that finally made first-person shooters make sense on a console platform, balancing the holy trifecta of guns, grenades, and melee, then throwing vehicles and multiplayer into the mix for the sheer hell of it.

Halo didn't reinvent the FPS, but it did exactly as advertised, evolving the genre in ways that remain unsurpassed.