To follow Peris' lead...
I'd actually claim this shot as the most badass of the bunch:
[Blocked Image: http://web.telia.com/~u71301317/dm_archt/15.jpg]
There's a lot to be said for subtlety, and this shot I think by simply relying on the light coming through the skylights and the associated bounce has an atmosphere that actually beats the rest of the level, which gets a little heavy on saturation and color at points.
This is something Valve does extremely well - a ton of the level design in HL2 is incredibly simple, but the right light accents and radiosity pull it off in a way that looks better than the flashiest most detailed scenes in other games. I'm not suggesting you re-do the entire map to match this one shot, but it might be something to consider in some areas. The first shot Peris pointed out is another fairly strong one in this regard, though maybe a little on the saturated side (I think because you're coming out of that red room).
Also, I know some people commented on this shot before:
[Blocked Image: http://web.telia.com/~u71301317/dm_archt/17.jpg]
I think this is a fantastically awesome geometric idea and could be the strongest landmark in the map but the surrounding geometry doesn't support that very well (both literally and figuratively).
For starters, as awesome as the cut-through terrain is, the 8 (at best) unit lip at the bottom just doesn't cut it. I'd go for at least a 32 concrete support, like there's real effort going into keeping that ground up there. Ferret's general comment about thicker walls definitely applies, too; it's tough to know for sure without a real sense of scale but it looks like some of these walls and floors are in the 4 unit range, which is really way too thin - even in real-world building you'd not want to go thinner than 8 units for a wall, and typically in this sort of style you'd exaggerate things a bit more.
