I do like the ambiance of the game. My only gripe is the unhook/grab diamond button: I'm not sure if it's really required. Just grabbing the diamond without having to press a button would feel a lot smoother, and would have the added benefit of not accidently unhooking from the rope.
The unhooking is a great idea, but only really sees use in the later levels. It's easy enough in the beginning to just trip the alarm and get back to the top. I would suggest weaving in the mechanic somewhere early on - so that you can get used to the small platformer segments.
I quite enjoyed the game. Good work!