According to the site, Gran Turismo 5 will feature 1,000 cars. Of these, 170 are "premium models" and will feature interiors and damage compatibility. 830 are listed as "standard models" meaning that their model data comes from Gran Turismo 4.
Polyphony did not share a course list, but did say to expect over 20 courses, with over 60 layouts.
The franchise's physics simulation is being refreshed for GT5. The game can now express damage, showing body changes following collisions. The game can also display cars flipping over.
Modes of play include Arcade and GT Mode. Arcade offers single races and two player battles. GT Mode offers a world map, a My Garage, a car dealer, a tuning shop for parts and tires, a car wash, a series-based championship race that uses a points system, and license tests.
Online is making it into the game in full force. The game will feature an open lobby as well as private rooms. Players will be able to interact with voice and text chat. Content sharing includes an online photo album, online replay album, and YouTube replay upload capabilities.
Photo Mode will be returning with GT5. This mode is split into at least two areas: Photo Drive and Photo Stage. The former allows you to take pics on circuits. The latter offers up special stages exclusively for Photo Mode.
Gran Turismo TV looks like it will be evolved from GT5 Prologue. The GT5 version of the video viewer will offers video output to the PSP, a reformed user interface, consecutive playback, and "progressive downloads."
Car buffs will also be pleased to know that GT5 Prologue's museum will appear in the game with added information.
Other features mentioned at the official site include custom soundtrack support, an updated user interface featuring color icons, and face tracking. The face tracking will allow you to freely look around the cockpit.