The idea for this game works pretty well, although I get the feeling the whole "merge" thing was added in out of necessity, not as a core part of the game itself. In fact, it would seem like *not* merging and keeping your bubble small would actually be better!
The controls are straightforward but difficult to do with a mouse. Tapping a touchscreen would have been more natural, and the portrait layout makes it seem like that was the intent. Having some kind of keyboard interaction would have made the game much more enjoyable.
The graphics look nice, but I'm a sucker for the simple vector-style art :P
I like the use of public-domain music but the songs were so different it felt weird hearing one right after the other, and neither felt like they had anything to do with the game itself. It would make more sense to have music that invoked feeling of floating or flying. For example, lots of high-pitched wind instruments and ascending lines would work well.
Sorry if this comment sounds harsh, it is a good idea and I think you should go back and iterate on the work you've done so far!