I have never played a Kingdom Hearts game. I recently bought the DS Kingdom Hearts 358/2 Days (worst title ever) game, but haven’t played it. After the DDD demo, I don’t think I’ll bother.
It was terrible. The voice acting, the controls, the stupid Jet Set Radio style rail grinding, the camera which insists on pointing in exactly the wrong way at all times, and the seemingly complex fighting system (that appeared to be a bit like that in Eternal Sonata) is actually “mash X”.