Legend of Dragoon is an amazing game, you should try that out SYG...
and Ultimecia actually had a reason there... Ultimecia didnt just POP out of nowhere at the end... if u have been paying attention to the game during the actual gameplay, you should have seen some scenes where Rinoa stands there( at the end of the second disc after the fight against Edea) Ultimecia uses Rinoa and after that she leaves her body and make her go unconcious, she thought Rinoa could be the sorceress she was looking for and she was right... so Ultimecia is the creator of all the sorceresses and make them bad... there was a reason for Ultimecia to be there in the game... she wasnt just a boss that no on knew about until the end of the game... seriously if you dont remember start the game over and beat it again, ull be surprised... to sum it up, Ultimecia is there for a reason, Necron isnt at all... we never even know even a bit about him during the gameplay except at the end, Sephiroth i have no clue cuz i didnt beat the game yet and sin and Tidus's dad... well i think there is a reason for them.

btw, Raziel i just borrowed FF7 from a friend(HLomegasin)... im starting the game right now! and THEN ill see who i think is a better villain... so im not quite sure yet.