@Jboy
Yeah I did everything there was to do in FFX myself. Played over 150 hours and beat the final boss 'Nemesis' in that monster challenge arena. The battle took about an hour 1/2 because he 4 million HP. And my reward for beating him: a note that says "You are the one who conquered all" or something to that effect. Every Final Fantasy since FF7 has had usually at least 2-3 optional bosses (weapons) that are more challenging than any boss in the game.
FF7 - Emerald & Ruby Weapon
FF8 - Ultima & Omega Weapon
FF9 - Ozma & Hades
FFX - Nemesis & (others in monster arena)
FFXII - This game had maybe 8-10 optional which is the only Final Fantasy game I played where I didn't defeat all the optional bosses. Just wasn't really into FFXII to keep playing after beating the game. Hope XIII & Versus XIII will be better for me.
@Fatetoone
3 hours for one boss fight is crazy!