I just hope they use a totally new engine, and not an upgraded HL2 engine. I missed out on TF2.
I owned the original Pong and the first Atari in 1977, and have been gaming ever since. Half Life 2's engine is the only engine ever produced that makes me physically ill after about 5-10 minutes. I get hot and start to sweat, and get queasy, to the point where I'm ready to throw up.
Yes, I've tried everything, including low to high graphics, different fields of view, and even different driver releases... just something about the lighting in that game makes me sick, regardless of frames per second or anything else. Happens with all Source games, including things like the Might and Magic game.