I thoroughly enjoyed this game and would recommend it to anyone that loves a good puzzle-platformer.
The level design is outstanding, I loved the variety of levels and how every level had entirely different mechanics and tasks to complete. (Low gravity, time manipulation, giant characters, micro characters, coop levels, teleporters and so on.) The entire section of local coop levels is a nice addition too.
Some of the other reviews talk of lousy keyboard controls, I cannot vouch one way or another because I used a USB Xbox 360 controller and it felt well suited. After plugging in my controller all of the buttons shown reflected the corresponding controller key.
I liked the game enough to get 100% of the Steam achievements as well. I didn't find getting the achievements to be tedious or ridiculous like in some games.
The sounds and visuals in this game are fine. The music could definitely be more varied though. By the time I completed the game I had turned off the music and was using my own soundtrack.
Play through in 1 hour blocks and you won't feel like this game is too repetitive. I usually have one major game and two or three smaller games I am working on, I used this as one of my smaller games.