Yes, good first map. Even though they are right, it does look kinda
dull and boring. I can see you put a lot of time and effort into
(I hope) this being your first map. Keep up the good work. Some things
you might want to add a 3d skybox, also its a little harshly lit. Put
in some lights.

Yeah listen to $loph because thats all you can do to improve it.

make it bigger, more than some props and brushes inside a square
box, make it more interesting, look up renos tutorial on displacements,
make it into a small canyon if you will. Instead of those barrels why
not have some jagged rocks, there are some in the models section of
hammer. Don't make it look plain and boxy, have vertical and horizontal
constrast. If you have some fps still left over why not add some rain
and puddles?

kk i uploaded two screens.

EDIT

i also added some props and decals.

critics please.

Uploading some screenshots would be helpful. People usually
decide whether or not they'll download the map by looking at the
screenshots.