The best thing that I like about this game, is its graphics.
Every single level, character, enemies, background and platforms are well refined. Just look at the trailer and screenshots! It is exactly as pretty as the actual game itself.
It is a puzzle platformer with a little bit of action in it. There are a lot of ways to tackle all the puzzles, and a lot of different approach to advance the levels.
The story itself is quite interesting. The puzzles are interesting and not too overwhelming. The boss fights pose some challenge but not impossible if you get to know how to fight (or just checkpoint-abuse).
The flexible difficulty settings make this game suitable for different type of player. After you defeat one playthru, you can replay all the stages from the start again with your already-unlocked skills to get past the stages in different way, and to collect the experience vials whereby you cannot collect in your first playthru.
Multiplayer is best played with friends that has almost the same progress to avoid spoilers and trolling.
The achievements added quite a bit of challenge and replayability if you're going for 100% completion.
My score: 10/10