You get a three-part Disney-centric plotline with each narrative section playing out based on which of the trio of characters you're commanding. Each character visits the same cluster of worlds, all relating to Disney lore. It should become repetitive by the second time you see the same magical kingdom but each character is given entirely different objectives, meet entirely different characters, and often travel in entirely new areas of the world. Occasionally their visits will even overlap, with one character running into another and giving the other a run-down of their current situation. It's impressive in-game storytelling for a story that essentially amounts to stock thematic material from every game of the last few decades.
The primary difference between this game and any of the others in the series is a shift in the gameplay mechanics. New to the game are Dimension Links which are used to summon allies who will use their powers to help the player. Your character will D-Link with other in-game characters as you progress, temporarily providing you with a range of new attacks and finishing moves, replacing your old ones. You get the Command System which relates to a gauge that progressively fills on your screen in-battle. When the gauge is filled your battle style changes or levels up.
You get Command Board, a new feature that appears once you complete a world. The Command Board functions as a makeshift board game: a die is thrown and the player moves, with each space having a specific effect on your character. It can be used to power up attacks and level them up.
Beyond the noticeable gameplay changes Birth by Sleep supports six players in four multiplayer modes in the Mirage Arena. You can fight one another in a deathmatch, fight co-operatively in a Survival mode consisting of waves of Unversed, race competitively in Rumble Racing or play the Command Board board game.
All this makes the button mashing element feel slightly meatier and more involving but it's too early to say how the story is going to play out. JRPGs are always slow burners, so we'll have to wait and see if the plot comes together by its conclusion.
Kingdom Hearts: Birth by Sleep is due for release on PSP in September.