Very Very Not Bad
I thought the game was great. Very addicting. It's simple and from what I gather is appropriate for all ages.
Just a few suggestions if I may:
1. How about some bonus points (and notifications) for multiple enemies in the same bubble?
2. Maybe some special weapons? That would be cool. They wouldn't have to be real violent. Maybe some air tanks for one, where air supply isn't drained for a short period of time, like 10 seconds. The special weapons could be gained the same way enemies fall: just encircle them with the bubble-ray.
3. How about some experience points or money where you could use them to buy upgrades? Make multiple upgrades per price range so that you add a bit of strategy to the game. The player will have to use decision making and actual experience of playing the game to make sure they buy the right upgrades for the level.
I think the game is awesome the way it is, but these would put it over the top.
Thanks for making a cool game.