I liked Tidus on my first replay once I was older. He's still no Zidane, but he goes through a lot of character development and ended up pretty endearing to me. It also helps that his more mature moments are probably as a result of Auron being around to parent him. They actually have great interactions as a makeshift family.

Anyhoo, to the voice acting thing. Tidus' dub is definitely a combo of the voice directing--they've since said that most of them were allowed to do whatever they want, so even though the guy's done plenty of work (he even played the final bad guy in Tales of Symphonia, since an anon down thread mentioned it), it ended up being what it was. He decided to make the narration sound like an older Tidus looking back without any prompting, for example.

Yuna's actress was a VA total newbie who audibly improves in the sequel since they were also trying to make her lip-sync exactly to the dialogue, which was a general issue. I also though she fit her character, but she probably did have some growing pains.

I think the same VO director handled FFXII later on, so they clearly got somewhere. That game has a ton of audio issues, but the voice acting is much more fluid... and has dub Balthier.