358/2 Days. WHAT!
The game introduces a Customize feature where you can choose what moves you want which both affect Roxas and the Keyblades. You have a grid you start out with and in it you add items like Potions, Phoenix Downs, and Antidotes. You also add moves into it, for example: Roll, High Jump, Block, Magic etc.
These moves sometimes contain empty squares attached to them when you add them on to your grid. Eventually in the game you will find power ups to certain moves/magic/etc. You can add a Roll power up to roll farther and faster, a high jump power up allows you to jump higher or double jump, and so on.
During the game you will find that going through missions and through the story that you can unlock the other characters from Org.XII and as a treat Sora, Donald, Goofy, and Riku are unlockable as well. You cannot use these characters for the main game but after you beat any mission, they will become available to play in a different game mode in the main menu. You can go through every mission you have gone through slicing away with any Org.XII character and Donald, Goofy, and Riku.
The last thing I want to point out in this game is that they introduce a new character to the series. Her name is Xion pronounces She-Own. I don't want to reveal much about her but she brings a lot of character into Roxas' story and is another connection to Sora. You get to fight besides her and against her later on. Roxas develops a strong friendship with her and looks at her as a human while the rest of the Organization look at her as a puppet and wish her dead.
The sound of this game is brilliant, sound effects, voices, music all sound great and most come directly from the original Kingdom Hearts titles. If you are looking for a filler between the gaps of Kingdom Hearts and Kingdom Hearts 2 then I recommend you play this game. Just like Chain Of Memories, this will tell you exactly what is going on, where all the new characters came from, and how everyone connects.