A programming accomplishment with flaws.
First off, the way you managed to compact such a fun game into such a small package is astounding - I frankly am amazed. That said, I found the game to be a little too short once I realized I was done with upgrading. Really, its the upgrades that keep you going. Boss fights would be a nice addition - perhaps everytime you change bubbles, there is a random chance it is a really big bad boss? I felt the big shot moved far to slowly to be much use unless you were in very close, which put you at a risk that the tri-shot gun did not.
Overall, a great game with a great deal to offer that suffers from limitations.