Really good, but what other people have said is true. If arrow keys aren’t locked down and scroll the webpage, while wasd work just fine, better to disable the arrow keys completely. The stars to progress thing works, but there should be some give to it; needing 12 or 13 stars out of a possible 15 to progress means people are less likely to get frustrated on levels they can barely solve needing to be solved in the most perfect way. In some cases, they are not going to see some of the best parts of the game as a result because the level groups unlock in a linier order. Again, really clever, but just missing the mark.
The movement system works because it is grid based, and the graphics are good. The step counter is helpful and the camera controls are nice to have, though I never really used them. Some music may liven it up as well.
All in all, it shows great promice!