Tastey Pies is very correct when he says that Rikku is the reason that Yuna's personality has changed.

Yuna is an emotional sponge, much like myselfxD Her empathy (which causes her to soak up the attitude of the people around her) is why so many people in spira loved her so dearly when she was a summoner. She still has that, and it comes into play just about every time that you have to start a mission.

So Yuna's personality changing is very possible and even makes sense.

as for the game itself, I liked it. It gave me what I wanted after the end of ffx, and a bit more besides.

Sure some of the actions they take in there, as well as the dialog, makes me cringe from time to time, but so did ff8's graphics the first time I saw them.

If you have trouble playing it, try NOT TAKING IT SERIOUSLY. Think to yourself 'oh, well this game looks like it's supposed to be fun and hyper' then play it expecting it to be.. . hmm, let's say 'fun and hyper.'

It'll make it a lot easier, I'm sure.