Google Play Link: Doodle Wizards

This is my first game I've ever developed. Imagine a tower defense game where instead of passively laying down tower defenses you pick and choose the correct spell, determine best size and time to cast, and use a gesture to draw onto screen.

I'm worried the most about gameplay, since it was my first game I spent a lot of time writing a engine, doing artwork, etc that I may have let gameplay slide. Polish is another aspect I'd like input on.

P.S.  I used a lot of artwork from OGA as well as music / sound, theres a credits section in game.