I think its the fact that its in 3D now. Maybe I have some rose tinted thing going on with how I remember Starcraft but the 3D models in this game seem to stand out harshly from the environment in some cases (basing it off the above screens). The aliasing seems to give me this feeling, I think. Though, it seems like modern games tend to look much better in motion.
It's distinguished mentally-challenged in motion. That's the one thing I most distinctly remember from playing it. The move to 3D has upped the animation ante in a noticable way, and it makes the units and the environment feel like one cohesive whole.
The thing to keep in mind is that they are never still. The little idle animations, even something as simple as a ship bobbing in the vacuum, creates this wonderful visual cohesion.
I'm gushing but the game seriously deserves it. SC2 is a perfect example of art direction and attention to detail just trumping the FUCK out of any technical voodoo.