Very fun. Lots of strategy. It took me a few seconds to figure out what to do. That being said, some sort of in-game tutorial to teach the player would be good. Nothing too specific. Maybe on the first level "Hold the magnet to attract the ball" "Let go to release" that sort of thing. There was a good variety of enemies. The font on the "Wave 1" countdown is a bit extra large. Maybe not so big?