The number one thing that I notice about level design is a lot of people don't fully realize just how much time and effort goes into making a great map. To make a great map, you have to put a lot of effort into it.
To give you a feel for what I mean, the three CTF maps I released in the ThreeWave CTF add-on took about two to three weeks each to build. That's working pretty much every day on them until they were done.
That's a long time. Think about that.
I'm going to be a little hard on your map, but you asked me to comment and I can only comment to the standards that I use for myself when I'm making levels. Take these with a grain of salt (pun intended!).
First off, you need to learn better use of textures. Load every texture set and scroll through it--get a feel for them. One of the things I noticed is you used an animated wall texture for a bounce pad. I was quite confused why would a decorative wall display be sitting on the floor then I noticed it was a bounce pad. Use one of the bounce pad textures (they are in the "sfx" texture group) so those players can clearly see where they are and what they are.
You have walls that are simple solid textures that have no variation. This is, in a word, lazy and boring. You need to learn a technique I call wall layering. This is a trick you see in a lot of the CTF maps. I'll include a little screenshot here to show you (you can also download the simple map file I built for these shots):
This shot shows an example of wall layering. Each of the two walls is made up of several textures placed on top of each other. This gives the walls a very polished look and makes the map certainly not "boring." A good part of map making is experimenting with different textures stacked together to make interesting wall-layers.
This shot compares the simple multilayered wall (that I put together in a few minutes) against your wall. I would say it's a pretty big difference. This is what puts the art into level making.
This shot is with r_showtris on and I numbered the layers to show you the brushes that I used to construct it. As you can see, it's pretty simple. I used six brushes to construct the entire wall and just used interesting textures on each one to build a convincing and pleasing layout.
So the general rule is, break your walls up! Don't make walls a solid texture--cut them up into pieces and slap them together in unique ways. Just pretend your are making the walls out of Lego that's 128 and 64 units high and that the Lego has different textures printed on them. Just put them together in a neat layout.
Also, if you are doing CTF map, try sticking to colors for each side. Blue and grey/black for the blue team and red with brown/orange colors for the red team bases.
This brings me to another important thing about map design. Lighting. As I wandered around your map, one thing came to mind: where is the light coming from? There isn't any visible source of light. Light should come from a source, examples being sky, torch, lamp, etc. If you wander the id maps, you'll notice lights everywhere. You need a convincing place for the light to come from!
Even in the little sample map I show above, I slammed a couple torches in there to make some light.
The trick in Q3 is that textures emit light--the flame on the lights in the simple level I showed above throw of most of the light. Point lights (the little light entities) should NOT be the primary source of light. Primary sources should be the sky, touches and base lights. The point light entities should be used to touch up lighting and add additional spread.
You have some areas that are WAY over bright. Specifically the over-the-top read glow in red base. Look at how the lighting in my Q3WCTF1 map is done and you can see how subtle light values and colors and make effective lighting.
Some of the architechure is a little odd. Specifically the columns--they look cool, but what are they holding up? You should lower the ceiling or arch the ceiling down to them so they look like they are supporting something. They look kind of odd just sitting there with nothing on top of them.
You need to work on some of your layout. The bounce pad to the hole in the floor is just broken--I bounced on it five times before I got myself through the hole. This is just badly laid out. If you hit the bounce pad, you should NOT get hung up. There are two solutions to this--make the target of the trigger push further up so you get blasted up there with more velocity and secondly, make the hole bigger!
You might want to inset the bounce pad into the wall like a column. See the bounce pad to the quad in my q3wctf1 map--it's a cut out in the wall with a curve behind it. Moving the hole to the edge of the room and cutting a column may work a lot better.
With a lot of work, experimentation and tweaking, you could make the map look awesome and play great.