Being a fan of RTS games as well as XNA, I decided to test the game.
I like the fact that you are using IMGUI. The look of the game is very simple. Here are a few suggestions:
1. Include a tutorial or a help file, I did not play for too long as I did not really know what to do. (Am a dumb player. )
2. Few better tiles. I understand this is programmer art. You could try to make some transition tiles.
Once i know how to play it, I could come back with more feedback. :)