Excellent work! Very detailed, and the resolution, while resulting in some large files, is great for close in combats! As a suggestion for folks, if you have a decent graphics program, you can do some home brew resizing of the files to get them smaller. You'll lose out on some of the resolution, but the gain in file size might be worth it for you.
On another note, at the current size, what's the scale for these? That is, how many pixels is a five foot square (or hex)?
Thanks for the great work!
Morgan
PS. I'd also toss in my vote for other terrains, like winter. There's a Fallout adventure called "Winter of Atom" that would benefit greatly from some good wintery maps.