The clicks!
It took me awhile to figure out which button I was supposed to press, as it wasn't even a button really. While the design may have been simplistic, it helps that this is a pretty creative idea. It's interesting to just see the different kinds of things you can do with the mouse button. I will say the one level with the bat and two arrows is downright unbeatable. Mostly, it's enjoyable because it uses something simple in a game that has complex themes. At least it's satisfying when you figure out how to do it.