Cars

More than 120 cars have been added to the lineup, pushing the number of available cars to over 1200 cars. There is a large selection of cars now included in the game, including those from the popular FIA GT3 category that have become the mainstay of GT car racing today.

Over 20 of the world leading companies in the automotive industry have designed special cars for Gran Turismo, celebrating its 15th anniversary. Over the course of approximately 1 year, cars from each company will be provided one by one in the game. This is a festival of cars only possible to experience within Gran Turismo.

Tracks

Including 40 Locations, 107 layouts.

In addition to new tracks like Mt. Panorama, Silverstone, Brands Hatch, and Willow Springs Raceway, the popular original tracks Apricot Hill and Mid-Field Raceway have made a comeback in the series.

Variable Weather, Variable Daytime, Astronomical Simulation System.

An environmental simulation based on the longitude/latitude position of the track is performed for real life tracks. For example, the Le Mans 24 hour race in the game will actually simulate the rise/setting hours of the sun and night-time constellations in the sky from the event in 2013.

Online

Within [Community], players can create Clubs and gather together in club lobbies, host race events for the club members and much more. It is also possible to access a web browser version of the Community feature via the official website.Moreover, 

open Lobby is a mode in which you can join rooms that have been created online, compete in online races, and communicate with other players. Choose your preferred room based on race type, difficulty level, track, regulations, and so on. You can also create your own room, either making it open to everyone or just inviting your friends.Αnd finally, Quick Match is a simple online racing mode that lets you take part in events with pre-determined regulations. When each individual event is entered, player matching takes place automatically, followed by the race itself.

Career Mode

This is the main scenario mode of this game, where you begin from the entry level and gradually acquire higher level licenses. With a new system that allows you to progress by gathering a pre-requisite number of stars, progress in the game can be matched to your skill. Many types of events have been made available: later in the game there are particular events where the weather conditions change continuously. There are also events that recreate the feeling of endurance races in a much shorter period of time. Winning events will award in-game credits that can be used to purchase cars and parts.

(From official page "Gran Turismo 6")