I can see why some FF fans were disappointed with XII. It is a considerable departure from what we're used to, and not all the changes work quite as well as one would hope.
However, I personally enjoyed the game. I love non-linear exploration, and FFXII is practically MADE of it. And that new fighting system actually works a LOT better than the traditional turn-based one from previous games. It's just a matter of getting used to it, which is done in minutes if you try.
Also, I like Vaan as a protagonist. Granted, he has very little to do with the plot, and he's pretty much just along for the ride, exploring the world for the sake of it. But isn't that exactly what the PLAYER is doing?
If we were to explore Ivalice through the eyes of the more plot-significant Balthier, who has been travelling the world for years, most of what we got to see would have felt mundane and unimpressive, as Balthier has seen it all many times before. But to Vaan, who has never been outside the city of Dalmasca and the surrounding desert, everything is new. Everything is amazing.
So while the other characters are concerned only with advancing the (decidedly uninvolving) plot, Vaan has the same motivation as the player!