Simple, but well built game. It's even educational for kids.
Although very short, I did enjoy it especially since it is free with no ads. Artwork is great even if there are limited colours involved. Adobe air wasn't too much of a hassle to get installed but you're playing within seconds so it doesn't matter. You've got time.
Intentionally "classic" blocky graphics highlight this simple yet fun little physics simulation. Starts with a very good tutorial. A bit short, though; doesn't take long to get through all 40 levels.