I like the layout, but I'd consider adding a bottom (with maybe some lava/slime) to the pit-o'-death in the middle. This would allow people to rocket jump out if they were quick instead of making it instant death. If you do this, perhaps consider suspending a good item (RA?) over the pit.
I'd also consider adding a YA, or at least a bunch of shards, somewhere in the map. Right now, the RA is pretty much what the entire map revolves around. This isn't necessarily a bad thing, but I'd certainly get a lot of playtesting to make sure it works.
I like the grate near the PG to jump over, but you could make it a little more interesting by raising it ~16 units or so, and adding a crate or geometry on the wall on either side to allow players to make the jump--or, if you don't add anything to one side and make the jump one-way, put something quite good in the dead-end. :)
You have verts off the grid on your rock ceiling over the RG, causing the sparklies there. An arena file in the pk3 would be nice too.
More detailing is certainly necessary. My suggestion:
http://fps.brainerd.net/mapmodels.htm