Good:
Cloud of Darkness (though, with the somewhat accent, I felt it would fit Ultimecia better)
Cecil (Yuri Lowenthall actually gives a crap about his work, you can tell)
Tidus (ditto James Taylor Arnold)
Firion
Exdeath (GET THE FRUIT! MARBLES!)
Chaos

Bad:
Terra (the only voice I found to be BAD, not just unfitting. Someone put this poor dying VA out of her misery)
Shantotto (WOULD be good, except it's insanely distracting that she's the mom from My Life as a Teenage Robot)
Kefka (doesn't fit what I imagined Kefka as in FFVI, but then again, they just kinda messed him up in this game)
Kuja (see Kefka)

Yeah