Great game! As short as the demo was, I was engaged very quickly. Very smooth movement, and the visuals create an amazing atmosphere. The animation on the character is very well done too, I especially loved the way they flap their wings each double jump.
Gliding definitely felt the most fun. The double jump was useful, but while it feels great to do out of a glide, on its own it lacks enough force, I feel. It can also be used to get through specific areas very easily, albeit not as quickly. I'd recommend making the double jumps have more force, possibly with a limit to how many you can do, that resets each time you glide or slam into a wall.
I hope to see more from this project, it has great potential! :)