I think the biggest advice I can give is decoupling the number of orbs from growth - the increased size makes it more difficult to not get hit, to jump (floor detection is off there), and just to move around. The bows/arrows fire too quickly, and are too fast to really work with them. It would also be good to be able to see which orbs have been absorbed.
I think this is a good start as a game, and an interesting concept.