This game can best be described as a courtoom battle adventure game. Long thought to be too quirky for anyone not from Japan, but when the DS remake was released in English this was disproved immediately.

This game is about Phoenix Wright, novice defense attorney, and the player must help him defend the must unexpected clients in the most unexpected courtroom situations. As you question the witnesses, you must use evidence to prove they're lying and uncover the truth to get your client pronounced "Not Guilty" and at the same time find the real perpetrator.

The game is divided into two distinct parts. The majority of cases span multiple days and most days consist of an evidence gathering and a courtroom sequence.
First is the evidence gathering segment, as it's rare to go into the courtroom without first having inspected the crime scene and some of the witnesses. This segment plays a lot like an adventure game, as you must travel to different locations to gather evidence and speak with different people in order to continue. This usually ends in a situation where Phoenix feels he has gathered enough to defend his client with, but sometimes there's only so much you can do with the information you have at that point in the case.
Second there are the courtroom sequences. Here you must mainly cross-examine witnesses, to prove that they and the prosecutor are lying. The goal here is usually to find holes in the testimonies so that your client can't be found guilty without more investigation, and ultimately to find the true perpetrator.