I think the English dub of the movie wasn't very well done. The Japanese audio was a lot better. I rather keep reading the English lines at the bottom of the screen than listen to it in English.
The voice actor for Aeris sounded like an idiot. When Cloud and Aeris have the scene in the endless flower valley, and Cloud says he wants to be forgiven, Aeris says "By who?" like she honestly didn't know. In the Japanese verison, she says it teasingly, so the viewers knew what she was thinking.
Why did they make Caith Sith Scottish (or is it Irish?). Dumb.
Vincent's voice was okay, and doubled with his performance against the three spirits, he sounded like Spawn or something
Barret was cliche, Cid sounded like a
cowboy, RedXIII I can't recall...
Cloud's voice was serious, like he's in the CIA.
Sephiroth's voice wasn't bad, but I prefer the Japanese one instead.
Tifa was alright. When I played the FFVII game, I imagined she had a different voice, but her voice actor was a reflection of her "don't give up" attitude.
Other characters kind of sounded like they had a little bit of a lisp.
Over-all: Japanese audio better than English.