It's pretty fun. Although I kinda liked the first game better because everything was completely new. The story, you also had fun learning about the new characters for the first time like Sora, Kairi and Riku. You had played something you never had an idea about. It was also fun meeting the Disney characters for the first time. Now in KH2 they're not that surprised to see you.
But right now I'm only at the collisium so I haven't really got into the game that much to know if it's better or not. I'm still looking forward to everything Tetsuya Nomura had to give during those 4 years. I just wished you could exprience the game the same way as in the first game.