K, it's a cool map with a rather interesting layout but more room is needed IMO: the main problem is a 'bad' flow due to this lack of space
For example, the lateral entrances to each flag-room are seriously hindered by the collision settings of the grass. The lateral passages are very narrow because of the lava things (whose damages are far too much high btw: you almost can't escape them...). The Health Vials you put up there in these passages are useless because of the damages from these sorts of electric fields. The doors on each side of the flag rooms are really slow and break the run, you should have made them faster or put only one instead of two. Etc...
Otherwise, it lacks of z-axis IMO: more variations in heights would have been welcome. Most of the time you're at the same height than your opponents and it's not a good point: it's better to allow players be at different levels, like this you introduce a more tactical aspect into the game in giving to players the possibility to get a more advantageous position against their opponents
Also, though CTF work better when the map is symmetrical in length, you don't have to do it symmetrical transversally aswell
This will allow you to put more variations into the design and therefore to increase the tactical qualities of the level in the same time
Visually, it's rather blocky and cubicle though some parts are rather cool-looking in architecture (the U-Dam location for example...) but overally lighting really needs work as well as sound effects btw. For example, you can use the opertures towards the sky to drop some cool light rays on the ground and on the walls... Things like that
There's a list of usefull links in
this topic: I strongly recommend you to read some of them before making another map and to consult them regularly while working on a project. Also, looking at other mapper's levels can be very instructive.
Good luck on your next project