Rich storyline, flashy gameplay, but severe button smashing.
Kingdom Hearts II did improve on a couple aspects. The gummi ship wasn't total death, and the storyline took a slightly darker turn. Some say they like the camera better, but I had always been an expert at controlling the camera with the L and R buttons, and in the midst of button smashing, I hardly had time to move my thumb to the right analog stick.
That is the greatest weakness of Kingdom Hearts II; the button smashing is endless. Sure there were "techniques"--like waiting until the green triangle icon appears and then smashing that button. In the original Kingdom Hearts, you had the option of selecting Ars Arcanum, or Ragnorok, but there were no such special moves in this Kingdom Hearts. Most abilities were just add-ons to the combo, creating the ability to stay in the air for a minute straight.
Button smashing makes it amazingly easy. I played it on the hard mode--proud mode--and had hardly any trouble, and I'm not even a core gamer.
Another improvement is that battles aren't only just kill the Heartless anymore; many battles have different things you must do like killing off the Nobodies while protecting the gate.
Drive Forms are exciting for only two times and then they're just shrug--offs. You do get to play as other characters, like Roxas, Mickey, and Riku, which--if you're a spaz like me--will excite you for like five seconds.
So if you're looking for amazing real-time gameplay, rent it first. If you're looking for an amazing storyline--go to Gamestop right now. If you just want some fun, get it and if you don't like it sell it on ebay and you'll only have lost ten dollars.