Original and balanced defense game.
I really liked the style of the game as well as the soundtrack. It has a great "feel" that sort of made you want to continue playing.
The difficulty was pretty much perfect. A challenge for some, not much for others. A good indication that it's in that magical little spot between too easy and too hard.
The tutorial was one of the game's weak points. There's nothing better than jumping right into a game and learning as you go through intuitive menus and informative messages. Those were also in there, of course, which allowed me to bypass the tutorial itself.
As previous reviews have said, the towers weren't perfect. I pretty much abandoned the ranged ones in favor of ground units, which actually damaged the opponents. Also, if would be nice if your towers could somehow manage the center turrets. They got tedious as the game went on. Other than that, a very good game overall. Excellent job!