KH2 is horrible. Why? Well uh, let's see here.
Graphics and voice acting doesn't make a game good. (Halo anyone?) I do agree that good music is a given for any RPG, KH2 only had one or two decent tracks. When playing an RPG, if the story sucks, then the game itself pretty much sucks. Why would I play a 40+ hour game if the story goes nowhere? That's like eating cereal without milk (or, in KH2's case, it's like eating cereal with expired milk). I want to be as nice as I can here: KH2 has no story. The story can be divided into three parts: the beginning with Roxas, the Hollow Bastion battle midway through, and the World that Never Was scenes. Honestly, you can take out everything else and the same story could be told. Even still, when you do get past the filler (and the Disney Worlds in KH2 were, for lack of a better word, shit), the story itself isn't that good. It's just uninteresting, and I felt no attachment to any of the characters. There was no emotion, no character development, nothing whatsoever.
Next, the gameplay. KH2 is a game that lacks what must be a given in any RPG: adventure. KH2 literally takes that away. For example, you're in Twilight Town, and you want to go to the Train Station, the game will literally tell you "That's not the way to the Sandlot! We have to stop <insert uninteresting villain here>!"
Also, the game just isn't fun. It's far too easy, and why would I do something that poses no challenge at all? It's so easy to the point where it's just boring. It's not fun at all. The reaction commands do nothing to heighten the excitement, either. Whenever you're given the opportunity to use the reaction command, it doesn't take any skill. Why? Because you know exactly what button to press! It's not like God of War or Resident Evil 4 where the reaction command buttons are completely random. Also, since the game was easy, I felt no need to explore for the [lackluster] extras, no need to build up, no obligation to do anything. Since it was easy, and the story sucked, I felt the only thing I could do was put a more enjoyable game in my PS2.
Some may argue that KH2:FM+ fixed the problems the original had. But let's get real here: if you have to re-release a game in order to make it better, it's obvious that the company has some issues at hand. But that's an argument for another time, I suppose.
In conclusion, KH2 basically killed any liking I had for serious. Ever since I played the sequel, I've felt no need to play the first one ever since, which is disappointing, because the first one was actually an enjoyable game. Also, I've lost any interest in the future games, which now I think the series is being milked. I'm just disappointed I wasted months of my life anticipating a mediocre game. That's all KH2 is: a mediocre game. Nothing more. IGN, I think, was being nice when they gave it a 7.6, because I think the game honestly deserves only a 4 or 5.
And that, my friend, is why KH2 sucks.