You've reached the end of the world, go back
few things this desperately needs:
1. a mute button, for the love of
2. P = pause
3. high score/submit score
some stuff that would be cool:
when you eventually get to the state with an orb around you, you should be able to keep growing untill you take up about 40% of the bubble arena you're fighting people in, then when you leave that arena bubble after killing everyone, instead of going into the one next you, the camera zooms out some and you get to start battling arena's, and so on. where the game would just be ever expanding.
I'd suggest keeping the screen clear of any interface (like it is). put all that extra junk in the start menu for when they hit pause (mute, current score, save game)
and maybe have a way to see how many bubble points you are away from leveling up again, cuz I'm like 110% sure I'm done leveling up right now, but there's no way to be sure, other than to go to every single room and kill everything (currently at the NW corner of the map). it doens't have to be represented numerically, like 150/500 or 85%, it could just be a big bubble with a little one in it that's slowly growing as you collect more bubbles from killin' stuff.
you should be able to eventually do everything that all your enemies can do, keep growing/evolving to adopt their powers, even have a red shell for a while (like when you're so big you take up most of the arena, just before you out grow it and start fighting the arenas). once the camera zooms out and you're so big you're fighting a room your next upgrade could take away the red shell, and those giant red bullets that come out of your butt wouldn't be so big compared to fighting the rooms you were just in. so the game could just continually evolve and grow, since the big bullets are now small, you can keep leveling up to bigger ones.
with a save function, you could save your character to come back and play where you left off, or even battle against other people in the online multiplayer zone to see who has the biggest strongest guy (there would be lots of room for ideas in multiplayer)
anyways, I'm full of ideas, hope some of those will help make something cool, but mostly, just put in a damn mute button