For the multiplayer maniac... Gears of War (read our review)
Gears of War is game of the year on a system that's only been out for a year, so we didn't have to think too hard before adding it to our holiday buyer's guide. But you shouldn't pick it up if you're expecting a deep storyline or engrossing character study. This one is all about the multiplayer.
You haven't fought a virtual war until you've been in those gritty, mud-drenched trenches with a battle-hardened buddy at your side, or at least over your headset. You're not a team player until you've risked sniper headshots or Hammer of Dawn meltdowns to rescue a fallen comrade. And you definitely can't say you've bested an opponent until you've chainsawed that opponent clean in half.
If you're mature enough to handle the gore, you need to be online playing Gears of War.
Runner-up: Rainbow Six Vegas