A nice looking game and unique take on the theme, but the theme-fitting mechanic didn't show up until level 11. the first 10 levels were incredibly easy with 1-4 enemies max, and then level 11 introduced the mechanic with no explanation and like 20 enemies. after that I never saw the mechanic used in a different way.
I'd like to see a better difficulty curve and overall flow. right now, all levels are either too tame or too hectic
Edit: I still say it would have been nice if the tutorial was integrated into the main game, and the new mechanic was introduced at a less hectic point.