I hated how linear and repetitive the game was. It was a simple 'beat the level and go to the next floor' kind of setup, and there were never any towns or chances to do anything besides battle. Not to mention the levels were all the same thing with a different appearance. It would have been very nice during gameplay to encounter some variety here and there. The way all the rooms were generated on the spot depending on what card you used, and how similar they all were really took away from the game and made the worlds not feel like they did in KH.
To comment on some of the other opinions expressed:
I actually enjoyed the cutscenes in the game, for mainly two reasons: They gave the player a break from the constant, repetitive gameplay, and they moved the story along. And I was really wanting to see where the story of this game was going.
The card system I thought was pretty okay. It was nothing revolutionary, but it was a pretty unique way of setting up a semi-action, semi-RPG battle system, and I liked that. In my opinion though, it was more complicated than just about anything in KH, and took some practice to get used to and use properly.