The director of Ghost Trick explains some of the fundamental concepts.
Ghost Trick: Phantom Detective Director, Shu Takumi, recently answered a few questions from Siliconera, making comparisons to the Ace Attorney series and explaining some of the decisions behind the story of Ghost Trick.
The lead character Sissel is a ghost who has lost his memory and through the course of the story changes fate as he rediscovers his past. The reason behind using a ghost for the main character is to create a more continuous story that allows the development of many characters. Ghost Trick includes over 30, and Takumi felt that a normal human couldn't become involved with so many characters. This contrasts with the Ace Attorney series as the characters tended to appear in separate cases, and as a result did not have such developed backgrounds.
Takumi goes on to talk about the design process for the characters, and mentions why a timing element was added to the gameplay. The full interview is at Siliconera.
Capcom recently posted drawings and video of Shu Takumi's artwork. The Ghost Trick drawings, and video of Takumi working on a sketch can be found on Capcom's blog hub, Capcom Unity.