So much to choose from.

The disneyesque dialogue

The fact that the game felt so confined and linear; it felt like more of a charter bus tour than anything is the only way I can describe this. You go to an area, do stuff, and never really have much of a reason to come back afterward except for capturing monsters.

Tidus, Rikku, and WAKKA. Ya? Ya? Ya? YayayayaSHUTUPALREADY

How about I just put the things that didn't annoy me.
-The battle system
-Most of the music
-Auron
-Jecht
-Blitzball