Halo Reach (Microsoft, XBox 360) [$59.99]
It's hard to imagine an Xbox 360-owning shooter fan that doesn't own Halo: Reach at this point. Reach is the latest entry in the franchise that's all but synonymous with the format, and it's refined to the point where it is as Halo as a Halo game could possibly get. The campaign is appropriately epic even given its futility, and the multiplayer is as smooth an experience as can be had on the Xbox 360. Find a group to play through some of the newest multiplayer modes, and there simply isn't a more fun first-person Xbox experience for a teenage gamer.