Very good game
The only negative aspect is that the medals are incredibly repetitive. Perhaps rather than making on play the game with all the different characters, make few playables and add more levels with some secret rooms or something. By the time I got the last medal, I was practically an expert, able to beat the game without dying even once.
Compliments are in order. I loved the consistency of the game world, I liked the different playables, and the game physics were well made. I had fun using the moving platforms to zip across the screen. The foreshadowing was also well played, giving nothing away but certainly having meaning to those who found the true ending.