One of my new addictions. I've solved all the existing levels (those last three are a bitch!), and I'm considering signing up ($10) to play levels created by others (and making my own).
Right now, I'm replaying each one trying unconventional methods - intentionally making it harder on myself. For example, if it's just a matter of building a car that takes the pink ball into the pink zone, I'll try making a catapult to hurl it instead.