Being produced by Yuji Naka.
Link: http://www.the-magicbox.com/0505/game050516j.shtml
Edit by big_smile:

The game is indeed being produced by Yuji Naka. In a Japanese press release*, Naka explained that all of Sega’s divisions regularly conduct research into developing the graphics of video games. The advancements made possible by the next generation of hardware allow Sega the opportunity to finally apply their research in producing new games.
According to Dengki Online, the Fifth Phantom Saga is a first person shooter (even though the screen shots seem to suggest otherwise) and fully incorporates the advance graphical and physics capabilities of the Playstation 3*. The physics simulator "NovodeX", produced by the U.S. company AGEIA, has also been used to enhance the realism of the physics in the levels.


The name is only a tentative title at this stage.
More information can be found at Dengki Online, Game Watch Impress and Sega Japan
*Disclaimer: information obtained through machine translation and so may be partially inaccurate
Update by big_smile
Sega Japan have released a website for the game, which can be found here
The genre is listed as "To be Revealed", so it may not actually be a first person shooter.
Update by big_smile
IGN have just posted some early impressions and a trailer of the game. It seems that Fifth Phantom Saga is a First Person Shooter, but 'innovates' the genre by adding a flying phantom, that follows the player, a bit like Tails in Sonic 2.
The player can send various commands to the phantom which range from breaking down walls to collecting items, allowing precious ammo to be conserved.
The E3 demo was from an early version of the game. It appears to contain few action sequences, but does have some puzzle-based sections.
The trailer focuses on the mysterious phantom creature.