I really appreciate your thoughtful and helpful feedback. I know the aesthetic is weird, which is a result of coming up with a workable idea for a 10 day game jam and then trying to build from there, steaming ahead, no looking back. Being limited to free assets is the reason for the old public domain art. I'm not much of an artist, so I had to figure something out. And the bright, garish colors went against my initial idea to make everything dark and gloomy and chthulian, but once I made the bubbles in bright, primary colors, I found the gameplay to be a little more satisfying. Again, thank you for both taking the time to play the game and to give such generous feedback!
And yes, the flying level is the last one, and I probably made that too difficult. Unfortunately, I found out that every one of my levels can be played on mobile except that last one, so I should probably get rid of it. Good luck with your projects!