My favourite part of this game was probably just the fact that you have to plan your movements taking the key into account - and you can use it to get up higher by jumping and sliding the end over a platform. So many times I thought I was stuck and then realized I could get out by popping the key over the edge of a platform :D Quite satisfying!
The power ups are cool. Add some extra dynamics to the gameplay. I liked the bouncy one ^_^ (I went there first too! Not sure if I was supposed to or not? I just walked to that area). Didn't get all the diamonds sadly, was missing a few, but gave it a good shot! Didn't experience any crash or anything as other people have - so that's good :)
Must agree with one of the guys below - screw the rats :D