Nice little strategy game there! It doesn't look like a fast-paced game at first, but I was wrong, haha. It was only until I read the description of the game that I understood what's going on. :) Maybe a good in-game description or tutorial will help a lot for future players. Some tweaks that could make an improvement to the game-play is adjusting the gold needed to build stuff and shoot, adding health to the base, etc.
Overall, it is a very good game!
P.S. Yup, I think it can be a good little mobile game, but of course it needs more polishing and some more contents. :)