Honestly a really unique idea and great presentation on the main character. I love the puzzle aspect, chomping up my glass bits to make myself big and strong and then breaking down to traverse tiny areas. Would love to see this mechanic expanded on.
Glass pickup can be a little finnicky, sometimes it can clip into terrain or just not be picked up. It also is sometimes unclear what glass break height is vs what death height is, so maybe some sort of visual indicator on the bird would be great to have.