The setting for the game takes place roughly one year after the events of the first game.Like the first game, the first trial is a tutorial one that guides the player, Phoenix Wright, into all of the elements of the Ace Attorney courtroom. This is established by having Phoenix receive amnesia due to a head trauma. The remaining three trials are united by the mysterious disappearance of prosecutor Miles Edgeworth.

Justice For All plays similarly to the first Ace Attorney game as a visual novel/adventure game. While the game has been adapted from the GBA version to use the DS touch screen, none of the special investigation techniques introduced in the "Rise from the Ashes" case from the first game reappear.

A small but significant change is that a player can now present the profiles of people involved with the case, in addition to the evidence in the Court Record. The player can present them either during the court room or investigative phases.

Justice for All features a new gameplay concept called Psyche-Lock. Phoenix Wright has to unlock several locks that have been placed over a witness' heart in order to reveal the truth.

[Edited from Wikipedia]