I definately can't wait untill Halo 2 comes out. I think that most people haven't really seen the 8 minute gameplay video and think that Halo 2 aint gonna be great, but their totally wrong, it redefines a whole new genre.
Other gmes I'm looking forward to are True Crime: Streets of L.A. A game that follows the same line as GTA but you are in a huge city (300 square miles), whatever you do affects your outcome, the combat is better than GTA, in GTA you could only do a few kicks & punches but in this you can do loads of different moves.
Half Life 2 - Played the first one long time ago and I think it was the best game I played on my PC. I'm sure the second will be even better
DOOM 3 - I think this is going to be great because of the sophisticated graphics and the actual gameplay, the thing about scaring gamers sounds kind of cool and physics is also well developed
Splinter Cell: Pondorra Tomorrow - I'll be playing this in March if the makers keep to their promise. What I think is going to be a great add-on to this is the multiplayer, can't imagine how it will be like but sounds great.