The googly eyes following your mouse on the title screen was delightful. The intro story was well done and the music helped give the game an epic feel. The way the bubble moved when you hit the sides or bounced off enemies and were knocked outside of it was a cool effect and added to the watery feel of the game.
The game play itself, unfortunately, felt unintuitive to me. Sometimes it seemed like I could be hit more than once before respawning, other times it seemed like a single hit would result in respawning,. It's possible that I was hit more than once in those cases, but it wasn't always very clear. It probably didn't help that sometimes hitting enemies caused the player to bounce around while other times it did damage.
The player's health vs. the bubble's health was not the clearest. Reading your reply to Dac helped me understand the connection, but it was very easy to miss in game.
It was also really easy to accidentally select a level up bonus instead of picking which one you wanted. Maybe adding a "Level Up" screen first and then the selection screen, or including a continue button on the selection screen could help decrease the chances of accidentally clicking through it.
I enjoyed the overall look and sound of the game, which made it easier to play through multiple times to try to get a better understanding of the game play.