~Great learning curve.
~Challenging extra levels.
~A little sensitive.
~Unlocking the puzzle mode.
~Exclamation Blocks aren't consistent.
I gotta say, this game is really good...much better than Meatboy because it isn't brutally hard or impossible. The bonus levels at the end of each world are pretty awesome, too (except the last one, that's just cold). However, the collision detection feels a little too sensitive (did I really just hit that lava?).
My overall complaint is starting the Puzzle levels. I want to see what's in them, but I've given up trying to beat the final challenge. It requires absolute precision and an exact path. Those take away from the challenge and make it unnecessarily hard. One thing that also makes this final challenge difficult is the Exclamation Blocks' patterns don't restart when you die. I may have the right path down, but it doesn't mean anything if the Block is solid.
Perhaps instead of requiring all 5 challenge stars to unlock the puzzles, why not 4 so that if someone gets stuck, they can just come back to it later after the other levels?
Don't get me wrong, this game is great. It taught the game in a good way, and the difficulty curve was perfect.
Overall, great job on gameplay, but I'm disgruntled with the stars.