Doing well seems mostly dependent on lucking out and getting an easy run, and not one where you jump to your death without being able to see what you are jumping to.
Needing to click on a nearly invisible door with no indication that you would even want to look in that area = very bad. Needing to click the same thing twice for no apparent reason = also very bad.
Incomprehensibly baffling. Don't take this as "it has hard puzzles". It just doesn't make any sense - no idea how to proceed or what you are trying to accomplish, no way to tell what's important from what isn't.
Early levels are a lot of fun, but the last two courses are frustrating to the extent of feeling completely pointless. I'm so sick of redoing the same levels.
A little frustrating trying to find the last few mushrooms (and deal with the snake), but the enjoyable gameplay and magical feel of the game more than makes up for it.