1. I guarantee that the massive framerate drops on web are because you're using a physics-based shatter effect, which isn't necessary--you could create shatter sprites that have the same effect, or use a more efficient algorithm.
2. It's hard to tell which direction the cube is facing.
3. Even though you said it's "forgiving," it's really not--there's more than a few puzzles which will auto-kill you if you miss a jump. Examples would be hitting a spike and being launched into a row of spikes, falling into a pit with walls too high, not being able to dash when over spikes--honestly, that last one is a big deal. Not being able to dash when over spikes? Think of all the 'saving throws' that could be made if you could dash when you're about to hit a spike. But no.
That being said, the music was great and the puzzles were, on the whole, pretty good!