This seems like a very good game so far. Definitely not too easy, especially on the diamond runs. I haven't even gotten to the point where I'm picking up gears (without it trapping me) yet. I haven't run into the problems other people have talked about with lag, even though I'm using Chrome.
I had no idea what I was supposed to do at the first boss. Only after looking at the walkthrough did I realize the point was to find ways to stomp its body/tail.
The only thing I don't really like is the mechanic where if you go from one face to another by ascending, and then cross into another face by moving sideways, then gravity rotates. It seems like it ought not to do that, so it's giving me fits. But maybe my brain will adapt to that instead of what I think should really happen (I realize the definition of what should "really" happen if you're a two dimensional man walking around on the surface of a cube and pushing it around in a three dimensional world with gravity is somewhat subjective).