you know, i like it. something i'd suggest is re-routing that river to go to the other side of the map and adding a bridge - everyone likes bridges. make sure it's big enough for vehicles to go over without too much difficulty
which reminds me: you've got lots of SPACE, but it actually looks very hard to maneuver vehicles through the field. i'm not sure how much you use them, but here's some tips for whichever end of the spectrum you lie on:
- if you're using lots of vehicles, leave at least two obvious routes for cars and tanks to drive through. you don't need the actual road plates, but just two corridors walled off by mountains and buildings are great. for every path that you designate as infantry-only, just start piling random briks over where you don't want cars to go. they make natural roadblocks, offer cover for infantry (marching soldiers on a paved road is a tactical no-no), and it looks pretty.
- for a more infantry central approach, random bridges from point a to point b are excellent. skinnny, crappily built structures are just begging for a demolitions expert, and those buildings with mounted guns lend themselves excellently. all i'd suggest is lay them out in better positions; that platform with the red gun battery on it isn't going to see too much carnage unless it's covering dead-center, and the space to the south of the treehouse looks a bit bare (i'd suggest just a random wall here).
regardless, this is better than i could make with my limited resources. with the current setup, all i'd change is putting a bridge over where those two island like things are, moving that ice fortress a bit, and just laying random crap all over where vehicles do not tread (like just below the southern river bend. there's an empty field that's surrounded by rocks and highlands).