Howdy!
The hub world is a really cool and creative way to give the player a tutorial and and level selector in a two for one combo pack. I definitely agree with the other comments though - more teaching is required. It felt kinda bad to be ascending and get killed by a spike you couldn't see until it just barely came on screen. I really loved the game design, and the art style and sound were very pleasing. I especially liked the detail you added after every gem capture. Great job, I had fun!