Really outstanding art and sound! The UI is very stylish and meshes so well with the music.
I didn't see a reason not to just defend/upgrade the same room over and over but maybe I didn't play long enough for that. But even then, the ammo system was a big pain point for me. It would be nice to get more ammo per purchase, as it seemed like I would never be able to reasonably buy another turret.
Balance issues aside, this is such a good game!