But the Half-Life 2 is probably going to focus on putting more than one character on screen at once

I still think that HL2 is looking mightily impressive... the movies do show that the characters themselves have emotions and expressions that have yet to be matched by anything I've seen in Doom 3... but like someone said earlier, they both have completely different engines... one is focusing more on indoor environments with extremely detailed lighting and shading, while the other is focused on high detail outdoor environments with a large amount of characters on screen at once.
Doom 3 is just more impactful because of the lighting, while there doesn't seem to be alot of detail. Half-Life 2 is putting as much detail as they can into every little thing.
I guess it all depends on what your tastes are. Do you like fast paced, eerie, scary shoot-em-ups? Or do you like drawn out story lines with very deep characters and plots, with dramatic scripted events and movie style acting?