I really like the colors and the whole metroidvania experience. And how the backtracks are always improved by your newfound ability.
The music is also very good, and so are the bosses. I love how their life meter was somehow "part of the scenario". The last boss fight was particularly very cool, with all diferent movements combined from the previous bosses.
I had a little bit of trouble using the bubbles/rocket in conjunction, so I'd usually stick to one or the other depending on the situation. Also, the arm felt a bit useless after the first boss, as it does nothing movement-wise (AFAIK) and deals no direct damage to enemies.
Also, quick question: Do you know if it's possible to sequence break and not get the bubble? I feel like I could almost get past the screen that first required the bubble without it, though I have no clue if the remaining sections of the game could be beaten with the rocket alone.
I enjoyed it a lot overall, this is a solid entry. Good job!