Not bad for a first map. Some bits of constructive critisism for you:
• Its a bit simple. Yes, its an arena type map, but things still look a bit plain. Detail is good, try to add as much as you have patience for, and try to use different lighting/textures to theme areas of the map a bit more.
• Lighting. As a general rule aim to use shaders for lighting when possible, as they tend to look nicer and feel more natural than ghost lighting.
• Jetcamping (or even just sitting on the roof with an md) might prove a bit of a problem here, as it is a very open map. An underground route from one side of the map to the other would be worth considering.
• I think the layout of the bases could use some reworking. In both bases the entrance leading into the tunnel is not very well covered, and in the alien base there is a line of sight to the OM from there. In the human base, a dretch/basi can wallwalk to avoid the turrets and sit behind the spawns picking off humans as they materialise.
• Non visible faces should really be caulked so the renderer doesn't have to draw so much. Select faces to texture rather than just whole brushes.
