Wow, you people love to complain over nothing <.<
Just face facts, the bosses most of you are complaining over are at least decent, or have much better "secret optional final boss" alternatives, but after going all the way through a game you enjoy there's almost nothing that can satisfy you for a final boss just because you've hyped yourself up all the way to that point.
That being said, the closest you can really get to a "bad" final boss is if the true final boss of the storyline (not including optional bosses) more or less cannot be lost due to whatever reason, be it it's a scripted fight or whatever.
Example: Yu Yevon of FFX, everybody automatically gets auto resurection cast on them. So the only way to lose the fight even if you were level 1 would be to self petrify your entire team. However, Braska's final aeon, the arena fights and the dark aeons (and especially pennance) more than make up for him.
@ Flying-emu:
To see the true ending, complete the game with all beam katanas obtained. If you do not have them all by the end of the game, choose to return to Santa Destroy, obtain them, and return to a bathroom to view it.