When Kingdom Hearts II was released in 2005, tongues immediately started wagging about its successor, Kingdom Hearts 3. An impressive cutscene following the final battle convinced fans that the third game, in what was assumed would be a trilogy, wouldn't be far behind.
However, fans the world over were disappointed to learn this cutscene was part of a prequel destined for the PSP handheld. While it is easy to approach this title with some trepidation considering its history, if you skip this title, you are missing out. Kingdom Hearts: Birth by Sleep may be presented on a small screen, but that doesn't hinder it from a sprawling scope that is on par (and even surpasses in some instances) with its PlayStation 2 predecessor.
The game starts off simply by introducing the player to the battle system and the game's three main heroes: Terra, Ventus, and Aqua. However, after some plot points, the player is able to pick which character they want to play through the story as. Although each character's story takes you to the same worlds, the events change and your interactions and dialog will be considerably different. You could get a basic grasp of the story by just playing through a single's character's story mode, but in order to get the full grasp and scope of the events of the story, a single playthrough with each of the characters is recommended.
The basic storyline in Kingdom Hearts: Birth by Sleep revolves around three up-and-coming Keyblade wielders who begin as the best of friends, but become embattled as one realizes there is true darkness within him. The story is simple and can stand alone, but there are some nice continuity areas that tie the prequel nicely to Kingdom Hearts II as well as Kingdom Hearts 358/2 Days. If you are holding out hope for a proper Kingdom Hearts sequel, I would pay attention to the game's secret ending as there are some not-so-subtle hints about the franchise's future dropped in the ending.
Although the game's story does make allusions to events from other games, the core plot revolves around the three main characters as they search for each other across the game's universe. Although you will see familiar areas like Hercules' Olympus Coliseum and Sleeping Beauty's world, there are plenty of new areas to explore, including the Enchanted Forest from Snow White and the Seven Dwarves and my personal favorite, Deep Space from Lilo and Stitch.