Hey nice work.
Pic 1: The building looks very square and the roof looks like a flat cap, put some sort of trip running round the edges of roof to give it more detail. You have to be creative and add more details, to look good it must have things that aren't there in real-life.
Pic 2: The grass needs some height and the shallow looks really steep, add some more levels (they don't have to be excessively dramatic). Use displacements. The grass texture should also be rotated to 45 degrees to help it to look less tiled. Use detail sprites!
Pic 3: Again, building very square, maybe give it a porch or something. I don't like the window cloths eithers, seem out of character.
Pic 4: Looks cool, add displacements to below the trees. Change the trim texture between the paths (rotate 90). Maybe create banked displacements on either side of the path, the create a path that stands 'proud/raised' of the floor. Change the tree types/skins, they look a bit similar - just a litle bit of variety.
Pic 5: The middle area place texture looks too repetative, create some variations of you own in photo shop. The lighting is also too bright for a night map I know you haven't finished yet, but lighting is one of the things that will make or break your map. Use dramatic shadowing intelligently. The platform (wooden roof) looks boring, just because it's wood paneling doesn't mean it has to be flat.
Pic 6: I think the window models are too close to one another, there should be a trim above, below and to the sides of those windows. I would create groups of 3 and intersperse them with sections of walls. I also doubt the brick texture would be on the inside window ledge. Think creatively about differentiating the texture using minimal detail. Take care with your windows, if they don't look right the building won't look right. The building should compliment the window design.
Pic 7: This looks good but I would change the texture of the floor it's the same as the hallway. Add a trim (again) to the bathroom. Think about drainage and pipes (don't go overboard, be subtle). I have no idea what that blue thing is!

The place /should/ be clean, use specular maps or boost them by editing the .vmf files.
Ok, the wall is broken, why ; how? If it was an explosion there should be blast marks or even an understated blackening and discolouration/carbonisation of the local area can add to the effect. How about a broken light that got caught in the explosion, a leaking pipe? The wall would also loose tiles and bricks, create a few tiles and scatter them around on the floor, maybe create your own model for a few tiles? (It's not that hard really, DL XSI

)
Pic 8: very square! The wall above the windows looks tiny, raising the roof is probably the easiest way. I know rebuilding brushwork is a pain, but it has to be done. Trim, detail - what is the room for? Break up the windows with a section of wall, the shadows will be more dramatic because of it. Basically more detail, HL2 props aren't going to cut it: beg, borrow or steal some more models. Failing that, build what you can with world geomentry and func_detail it.
Pic 9: Add a trim, sunken of gravel between floor and outside of building. There's a lightsource further down the building, where it it coming from? (use light_environment to get a good ambient level then detail with other lights.
Pic 10: Lightsource, trim, detail.
Pic 11: ?Kitchen? is way too small, way too grubby. Think about the processes of cooking that have to be done to create food for all those kids that attend that school. There's no workspace at all, things like extractor fans and a fridge section can add detail to your map both inside and outside (fans must go somewhere). Use trims etc..
Pic 12: More detail on buildings, better/more light sources that contrast colours an throw shadows. make an inside rail for the woodem roof- make it more interesting architecturally. Displacements.
Pic 13: Again more details, posters, white boards - interesting things that while might not be in your lab, are interesting. Rack mounts, things from a computer science lab, NOT Dr. K's - haha.
Pic 15: Loose the texure in the middle, it looks odd. I don't like the blue. texture above the doors is of a greater scale and doesn't match the wall. Don't use the same texture throughout! fix the bathroom like I said above. (Or don't, whatever you choose. :-])
The Rest: You will come to a point where you have to consider the visibility load, if the player's leaf can see all the others in the world - this will be bad. The map is small so it might be ok, but you may well have to compromise on detail because of it; which is where you creative texturing and economical use of detail and lighting is going to pay off. Read up on hints.
The window situation may become laggy depending on the players view, you could make it as detailed as you like, but if the player has to see 15 copies of them at the same time it will be bad. Use areaportals to get round this. Be clever, be creative, don't be afraid to remodel.
For the outside/borders use a combination of houses, woods and other natural and man made stuff to basically block the "walls" off, then use a cool 3d sky box and place the map inside what is like a dinner place, suggestions of valleys etc.. flat is boring! Moving clouds etc can help add depth.
I hope this helps, best of luck.