It's pretty cool, I like the visuals and the music is great. Did I mishear or is the soundtrack dynamic, changing with the enemy difficulty level or so? I'm a sucker for dynamic music.
I think the difficulty could use a bit of work though - there was very little challenge until I think around the time I got the third turret. Perhaps that's intended, but I felt it was a bit too long. Then suddenly there were swarms of enemies, but I was not really limited by money, but by my ability to run around and spam-build. I think it could start off harder and scale more smoothly.
And also a suggestion - when you unlock a new turret type, it would be nice to have some sort of message indicating what it is (maybe how much it costs?). Or maybe there is some info somewhere and I didn't notice it.