-Well you've done a great job on making the layout balanced. It's pretty cool.
-It's fun to play on with a small amount of people(good & bad)
-First off the map is too small for a good and large amount of people. Right now at best I'd say it's good for a 4 vs. 4 match.
-Second, it's too simple right now it just looks like you threw together a bunch of block brushes and made them into barriers, this could have taken no more than two hours.
-You used sky_day01_01 for a skybox which is a horrible and depressing skybox.
-All of your brushes and textures are too redundant. It's not good to fill your map with a bunch of blocks that all have the same textures. Especially mono-toned textures it just looks very bland and very bad. Gives the player a feeling of bordom.
-The walls surrounding the map are too close in to all of the action move them back a couple units and mix up the brushwork so you don't just look like you've got big grey blocks surrounding your map.
-The grass is also bland, add some very small displacements and also add some alpha's so that will give your ground a natural terrain appearance not just a block.
-Enlarge your map, make it so that it can have the capacity to hold maybe a 10 vs. 10 match or something like that, servers now adays are beginning to have a lot more player slots, right now they would have to many players for this map.
-Mix up your brushwork and change some textures around, add some props and decals, make your map sparkle. Take that blandness out of the picture.
-Bring the walls back from the map a little bit they're too close.
-CHANGE THE SKYBOX
-Add some displacements and alpha's to your grass, make it diverse.
Nice job, cool layout, keep on truckin'!