Wow this is great! Very innovative! It's very simple yet difficult at the same time. This game deserves some more attention.
Keep up the good work.
I looked at the How to Play option but I couldn't figure out how to get back so I had to reload the game.
Edit: Answered your questions.
For your questions:
1. About 10 minutes
2. It had a good ramp up of difficulty. I got stuck on level Daredevil
3. Innovative. Fun mechanic.
4. I don't know that there is anything I really disliked. Maybe some suggestions for possible changes. Blinking spikes were kind of annoying because I couldn't see them to time it.
5.
Currently I can only change gravity when I'm jumping, not falling. It might be nice to change gravity at any time I am in the air?
When the room spun it seemed to move me a little. Almost seemed like the room spun off center. There were times I would jump near a wall of spikes and the room spinning would throw me into them instead of me falling past them.