Half-life 2, without a doubt.
All I continue to hear about Doom 3 are the graphics, what about the story?!
Like HL, HL2 will undoubtedly have a killer storyline and killer graphics. One need only look at the screen shots to understand. Better yet, watch some video, the colors and lighting in this game is breathtaking and the idea of picking up right after the end of the first game is great. I'm not putting Doom 3 down (it too looks amazing); I just think HL2 is more of a complete package. I mean, at least HL2 has a release date instead of when its done.