A term used to describe video games in the FPS, First Person Shooter genre, that are believed to be the next big thing since Halo Combat Evolved.

when you're hungover as shit after a spending a night drunk as a skunk

A very high-quality shooting video game.

A console video game (a first-person shooter specifically) which is better than, or claims that it is better than, the games in the Halo franchise. Perfect Dark claimed this and failed, Killzone claimed this and failed. Call of Duty 4 is indirectly claiming this and might fail. No game has yet been able to claim the spot of being better than Halo, and to claim to be a halo-killer pretty much destroys any slim chance they might have had.

A game which is determined better than the infamous halo game by the gaming community. Not doom.