Great game! It's one of the most unique tower defense games I've played. My critiques would just be repeating what others have said so I'll talk about the art which I think is pretty well done. The environment has a nice style and the black silhouette-like design of the enemies is a clever way to make them contrast and stand out. I think that it could use more juice/game-feel though such as particles or a shader on the enemies that indicates that they've been struck.