Great gameplay but pretty poor flow. Almost stopped a few times because there were things I didn't know the game was capable of. A good example is the spike pits; there is no reason to assume they're harmless when walked over but harmful when fallen on, and even less reason to believe they can be fallen on when crouching but only inside a wall. It feels like I'm not learning how the game works so much as finding out the designer's bizarre idiosyncrasies.
Anyway, that's just about the rebound the average player would have on first playthrough. All those conditions to movement/traversal make the puzzles extremely fun and perfectly challenging.