You have done very well and it look like remind me of Desert Strike!
That is an image from Stronghold Crusader, I did not make that, but it is what I am hoping to acheive - or better.
EDIT: another benifit to 2d drawing, in the game I keep mentioning, you can press a key to lower the height of everything - buildings, terrain, towers, etc (to see things that would normally be obscured). In 3d that would require changing the position of vertices, and I don't think that would be fast, in 2d you could just change the global height differential and subtract it at draw time (this would also enable you to fade the height down/up - when said key is pressed slowly move up or down).
EDIT: Firefly's (company that made Stronghold) terrain rendering system is flawless, you can even change the rotation of everything onscreen (north south east west). Pretty funny if you compare Stronghold to Stronghold 2, Stronghold wins by miles. The 3d looks like crap in the second one.