I might download the map later, but let me comment on the screens first:
The sand on the right rock looks strange. Sand would not spread up so far I think. I know you are trying to get a smooth look with those alpha textures, but since the rocks do not flatten out towards the sand, I advise having a sharp edge between rock and sand texture there. What you can do is having the sand wedge against the rock at the base.
Another thing you might want to add is smaller rocks and pebbles at the base of the rocks.
CS:GO can use many more objects easily, so use the possibilities.
Add a few details, as some people mentioned. Just some ideas: add a group of barrels in front of the wall to the left. A broken down car might fit on the far right, in front of the rock, where the small bridge meets the rock. You can add scrap metal and cinder blocks and another barrel close to the tree. Use clip brushes to avoid negative influence on gameplay.
Yeah, well, really lacking detail. Do something about where the wooden supports meet the wall. Perhaps add pillars to the walls, on which the wooden beams can rest. Add a bit of junk close to the walls, perhaps a barrel at that wooden V pillar you already have. Don't overdo it though, as this is the hostage area. All stuff has to be carefully placed and you might want to use clip brushes again to avoid any negative influence.
Basically what I said concerning the first screen. A bit of random scrap metal, cinder blocks, smaller rocks and pebbles, stuff like this. That should be enough.
The visual style is nice, it is just it lacks a few details for a scenery like this.