First I want to say great game. Second I would like to make a couple of quick suggestions.
1. The information pop-ups that block the screen like "here buy this stuff" really annoying. It would be better to just have an upgrade section between levels, especially as you don't really say what the upgrade cards do (no it isn't obvious, the text kind of runs together. I mean I can guess that one was damage and one was armor, but I would rather not guess.
2. The aiming seems to step a bit making it hard to target a unit without moving your guy.
3. Having the guy off to the side, kind of annoying, yeah it is outside of the box.. it is neither first person nor third person, but I like the box.. The game could easily be first person.
4. there doesn't seem to be a way to get back to the instructions which could have been clearer. and there doesn't seem to be an option to just restart from scratch.
And that about covers my impressions. Once again great work, hope to see more.