I liked Yuna quite a bit, once she stops being Yevon's lapdog. Before that, though, she's not so different from everyone else, eating up everything Yevon has to say. But at the same time, I get that, because that's what EVERYONE has been doing for a millenia. This is where the comparison to Wakka comes in - yes, they're completely different, but I like that they grow and change as characters over the course of the game, even though I don't entirely like them, the actual people. (Although in Wakka's case, I don't like him, period, while Yuna has a number of redeeming qualities and I spend at least the last 15% of the game liking her quite a bit [though not as much as Rikku and Auron]).
What bugs me is that never did anything just for her. Not so much that she was selfish - more that she didn't do something JUST because she wanted to do it, for HER. She spent the entire game making sacrifices for everyone else, in large part because it was what was expected of her. She even says on the boat to Luca that it's hard following in her father's footsteps as a summoner because everyone knows who he is. She's agreeing with Tidus' sentiments about having a famous father, which can, to some extent, be explained by the radio announcer at the beginning of the game as you're walking along the road - people expect great things of you. To me (and this is my opinion - maybe I'm wrong, and if so, then that changes a lot), Yuna may have become a summoner to help people, but isn't she doing it because she's Braska's daughter, and that's what people expect of her? All eyes are on her, and she has to be absolutely perfect for everyone, because otherwise, they're all disappointed in her. Which means she has to conform to and live by what everyone around her wants to be, rather than just be herself.
Granted, a large part of it is because of Sin, but still. The only thing that Yuna does just for her is fall in love with Tidus.
...and then fast forward to X-2 where she flies around the world trying to find Tidus, which is something she does...just for her.
I can get over her being soft-spoken; that's not really a big deal. But I don't like it when people try to live their lives by devoting them to making everyone else happy, because it means that they themselves can never be happy, since their happiness thusly depends on satisfying everyone else around them. When do they get to live their life for them? There's making sacrifices to make people happy, and then there's slavishly following what they want you to do.
Even when Yuna runs off with Seymour, it's only to save her friends - NOT because it's what she wants to do.
Not that I'm saying she should be a selfish bitch, either. Just that her not really trying to live for her own happiness at all kind of bugs me. I don't like it when people don't do that IRL, either.
Edit: Especially when her actions are contrasting. Yevonic dogma is law to her...yet she sticks up for Tidus on the way to Luca, a guy she doesn't even know, and vehemently defends him from the Goers, who are making fun of him, and truly believes his story about being from Zanarkand. She believes him BEFORE she knows he's Jecht's son, when there's literally no reason to, especially based on what she's been taught all her life.
Paradox =/