The ending: comparison with Beauty and the Beast (SPOILERS)

When watching this something occurred to me: when Tiana and Naveen kiss they both transform from frogs back into humans. Now of course Naveen knew what Tiana looked like in human form, but Tiana did not know what Naveen looked like in human form. That's not the Naveen she fell in love with, she fell in love with Naveen as a frog. So when they become humans Tiana seems to accept very quickly that this is the same Naveen, she doesn't seem too hesitant to kiss Naveen as a handsome human prince.

Compare this with Beauty and the Beast when the beast transforms back into Prince Adam in human form, Belle takes a moment to look over him with curious eyes looking for any signs that this is the same person (or beast) she has fallen in love with. And then there's the moment of realisation when she looks in his eyes and says "It is you!" as she accepts that Adam is indeed the beast.

Something like this would have made that relationship between Tiana and Naveen just a little better and stronger.