Kinda fun, really pretty, and solid menus and intro. I was impressed with the drawing mechanic. The sprites were well drawn and the background was nice. One thing I noticed is that drawing with a mouse is awkward and uncomfortable, so the main mechanic, while cool, got repetitive. I want to see zombies blow up and the art work, not my hideous squigglings! I think it would have been a better experience on a touch screen.
If the mechanic was used more sparingly (like, to select spells, or maybe the spells had 50X more shots), I think it would have added a lot to the game play.