Not the best way to play a Kingdom Hearts game, but it's got a nice story and it's an interesting crossover.
The story line is really interesting. It introduced this new set of enemies we had no idea existed but have apparently been around the entire time. And it brings together all the old characters but has a first time interaction as they aren't really there. It also interested me to see how this young girl, Namine, was actually able to manipulate Sora's memories yet we had never actually seen her before.
Then it brought in Riku as he was able to find his way through the darkness to this castle that sits between light and dark. You got to see the other half of the story and a different point of view then what you normally have. Plus, we actually find out what happens to our lost friends in the darkness which hasn't been revealed before now. The game play with Riku is slightly easier since you can't change decks, they are all preset, but that can also frustrate you since you've probably gotten use to using the card combat system and want to customize his deck.