Kingdom Hearts: RE: Chain of Memories' gameplay is unlike the other Kingdom Hearts games. The combat is not hack and slash, although it is still in real time. You see, the combat, like everything else in Castle Oblivion is controlled by cards. That's right. Cards. So, in order to do almost anything you need the cards. Want to open a door? You need a card for that. Want to attack? Card. Cast a spell? Card. Heal? Card. You get the idea. Even the worlds you travel to inside of Castle Oblivion are controlled by cards.
You start out with a basic deck and it will grow from there. You can collect cards throughout any of the world rooms in Castle Oblivion by either hitting random objects, defeating enemies, opening chests or buying them from moggles.
Since everything is dependent on cards you really have to build your deck with care. The cards all have a number and the higher the number the stronger the card. Since even enemies have to play a card to attack you, the high card wins. So if you play a 3 and they play a 5, they hit you. If you play a 9, you hit them. You can even do multiple attacks by stringing 3 cards together (or buy special attacks when you level up). However, the 0 is the most powerful card in the deck. It can break any card, including a 9-9-9, if you play it at the right time.
Entering rooms is also dependent on cards and their numbers. In each world (you go to pretty much the same worlds as you do in Kingdom Hearts) there are a number of doors. In order to get in the doors you have cards (with number values) that you must use. Each door has a number assigned to if and you'll need a card that corresponds in some way to open the door. Be careful though, because the kind of card you choose to open the door with determine what is on the other side. There are cards for lots of enemies, few enemies, moggles and so on.
While it seems like a lot to take in at first, it gets easier the longer you do it. It does remove some of the freedom of just pounding away at enemies with Sora's Keyblade, but it also adds a nice bit of strategy to something that could just resort to button mashing.
The control scheme is similar to the other Kingdom hearts games. You control Sora with the left joy stick and the camera with the right. The left and right buttons control your deck, X is jump and O is attack. It feels pretty natural after you get used to it.
Also, the game has a pretty high replay value, sort of. Once you finish it playing as Sora, you can play it in reverse mode as Riku. Pretty cool!