First off, this MacUpdate page is misleading. This game is NOT FREE, it's a DEMO. You can play the first three levels for free, but you need to purchase a license to play beyond the third level. That pretty much defines what a demo is.
As for the game itself, BUY IT!
I play literally hundreds of games, and my favorites tend to be puzzle games. The problem with many puzzle games is that they tend to be more boring or frustrating than fun. And Yet It Moves is a FUN platformer/puzzle game. It's unique in some simple but brilliant ways.
Basically you run and jump your character through the different world levels, but the twist in AYIM is that you rotate the world and it's gravity to allow your player to make it through various terrain. It sounds simple, but they've used this twist in ways you may not expect, and it makes for some very unique gameplay that you haven't seen before.
My only complaint is that I wish the game was longer, and that's really just a reflection on how good this game is. And Yet It Moves is a welcome addition to the puzzle genre, especially for those who find most puzzle games lacking in originality and fun.