This is a really cool game. I like it!
I also like how the game forces you to collect coins if you want to keep going, just like the rings from Sonic.
However, I think the rising lava in the 2D style is too fast, at least for me (it's probably just my skill issue). Lastly, it's very difficult to tell where you're going to land after a jump in the 3D style.
Anyways, keep up the great work!