I haven't beaten this game yet, but I have been playing it on and off for a good while now. It is easily the best game to come out in 2006, and in the top 10 for PS2 games, maybe even top ten for games to come out in the last generation period. I find the levelling up system to be kind of frustrating. For someone such as myself, it's too in depth, and the fact that you have to level up the ability to use weapons, and then having to find them, to me that just plain sucks. I wanted to make certain people use certain weapons, but because you never know what weapons you'll be able to find you constantly have to compromise what you want your characters to be for what they can be. In the end most of my characters ended up being incredibly similar, using the same armor and the same weapons. It's just less of a headache to make everyone similar instead of figuring out who can use what and when they can use it, and as far as I can tell, it works just as well.
Aside from that though, this game is incredible. It's one of few games that really attempts to create a living breathing universe for you to play around in, and it does it incredibly well.