Couple of problems here, but i have addressed them in picture form!
This exit should be bigger, as it is quite difficult to drop through it.
couple of design issues here. there are some HL2 textures, (the floor and the brick wall) and there is a blue light in that hallway, not really fitting for a red base.
jumping of this area hurts you. The area should be lowered a bit so you don't get hurt when you fall down.
The sewers would be nicer if you didn't have to swim through them, possible solutions would be making the sewer rise up at the beginning, so that you can walk through the water without swimming.
This area should be player clipped of, as i can surf on it, which is bad.
There is a HL2 texture! i personally would make this arch opaque, it looks out of place.
This ladder works, but you have to jump up to get to climb it.. I would suggest making player clip stairs that are really thin, instead of climbing the tiny stairs on the ladder structure.
This vent is a bit hard to get to, so i would suggest making a catwalk extend over to. TF2 is not a game where difficulties in getting places belong.
An interesting concept, but there should be more signs and arrows informing the player to go here instead of their intel room.
Signs like "bring the enemy intelligence this way" would fit perfect.
Hope these help you.