Man! So many boss fights in this game, I tell you what. Er... Maybe a few more than I'd prefer, to be honest; you can pretty much count on one at the end of almost every area, even the optional ones. That being said I'm still enjoying it. I think I'm fairly close to the end (I've found all the "lost memories," apparently defeated all the story bosses, and have maxed out Naija's health) but want to try and find a few more of the hidden treasures before proceeding.
I do wish to register a complaint about Aquaria, though. When I started playing and saw all the giant-sized marine creatures and plants, it made me think that Naija was supposed to be about the size of your thumbnail and the whole grand world-shaking epic was taking place in a tide pool a few yards across. That would be awesome! However, later events made it pretty clear this is not the case -- she's quite normally sized. Ah well.