After seeing the BLU defend design, I had to give this one a run through. Too bad the cart and the home icon on the HUD can't be RED. Grr!
First, some screenshots of things I noticed:

I tried to capture the fire alarm bell there in mid fade-out. This was a general issue I noticed. Lots of props were fading in and out in a way that was quite noticeable and distracting. Just increase the view distance.

This wall I found kind of oppressive. I think it's just too much of that one metal texture. Also, the wood grain on the under side of that upper diagonal brush is, to my mind, running the wrong way.

Too much of the metal grating. I had this problem in my own maps. In Hammer I think it looks really good. But in game, drawing all those little lines on the screen looks crap.

I didn't understand this hallway. Kind of weird and doesn't really seem to fit with the rest of the map.

Now to the good stuff. I really like this room. I was sitting on the cart rolling through the map, and when I got here, it was definitely a "Wow" moment. Very cool space. Nice detail with the bomb moving across that conveyor.
And on that note, I think the map is too big. I know you said you made it big to accommodate lots of players, but with all of the different areas and tunnels and halfway check-points, I think it's too much. If I was you, I would cut out most of the exterior stuff, except for the roof ending---keep that. I think your best work is in the dark green interior space, shifting to the lighter concrete, and then to the spytech offices on the top floor.
Like I just said, I thought this transition from texture themes was beautifully done and nicely detailed. Again, my big advice for going forward would be to shorten/eliminate all the stuff that comes before those last 3 checkpoints. Maybe have RED start just outside a loading dock or something, hop on the cart, bust into the factory, and off they go, climbing up floor after floor to get to the roof. BOOM!