-snip-
Overall it was very fun and looked good.
The inside parts may look a little TFC-ish (not a bad thing either), but the outside definetly has the TF2 vibe to it.
Oh yeah and you may want to tone down the fog on the 3d skybox because the smoke sprites aren't afected by fog and it looks kinda weird.
EDIT : Ok so since you asked, a little more detail
1) I -think-
this is problematic : you can put a couple of sentries on the red crosses and essentially negate this route to the enemy. This is not a problem in itself, the problem IMO is the resupply room that is right behind it and makes upgrading a sentry really easy. On the other hand, it an enemy demoman or engineer camps one of those spots, you're in for some trouble, because that spawn room only has one exit, unlike the other one. The ramp is good and should stay here, it allows the defenders to protect one access to their intel and gives them a height advantage, but the resupply room may be overkill ?
Also about that ramp that 'leads nowhere', it's nice but I didn't find out about it while playing. Maybe put an arrow pointing up against the wall ? or something that vaguely hints that this will slide open ?
2) Detail :
this looks somewhat wrong, the slide door shouldn't 'cut' the tracks. Make it stop above the tracks and put some black brush behind the door to make it look like it goes beyond ? Add in some striped (yellow and black... thing) brushes on the sides of the tracks to make it look like the door isn't laying on the tracks alone ?
3) Could use the morphing tool
here
4)
Something looks wrong but I can't tell what 
(if it's done on purpose, leave it as is)
5) About that ladder, I see a posible fix
like that. Pushing the wall a few units back should give you enough room to place a ramp here. But then you'd have a ramp that starts on a slope instead of a flat surface, is it that bad ?)
6) Finally, on
those stairs, use the morphing tool, and maybe add a pillar somewhere or something so it doesn't look like they're 'flying', but then it might be annoying to movement/visibilty...