I really loved many of the mechanics, the fact that my character is melting most of all. The tutorial signs just don't work with the speed potential of the character. It's possible I missed it but the fountains usage didn't seem to ever be explicitly called out and it's just long enough that you may not stand near it long enough to trigger, you could also just make the fountain on the tutorial level much shorter and that might trigger it. I would also make sure to explain the effect that melting has on his friction, it took me far longer than I would like to admit to learn that, but once I did things were much easier, and I can definitely using the inverse of that later in levels (where you have to have a certain level of melt to complete a section).
Awesome game, really enjoyed.