I noticed kind of small changes to the different enemies you face, which was a plus. Controls seemed pretty good as well. Only thing that kind of got me was that the pattern was the same for each enemy. The enemies also only spawned from the left for me when I went to the far left side of the area, which made any difficulty null at that point. I'd say look into the spawning for that a bit more and you have yourself a good game.
I'd recommend adding a list of buildings that can be constructed either in the description, controls, or some in-game menu as well as a description for each. Other than that, it seems like a pretty good text strategy game.