Here is a brief overview of the game, via its store page:
Dynamic seasons change everything at the world’s greatest automotive festival. Go it alone or team up with others to explore beautiful and historic Britain in a shared open world. Collect, modify and drive over 450 cars. Race, stunt, create and explore – choose your own path to become a Horizon Superstar.
Forza Horiozn 4 is due out for Xbox One and PC on October 2. Users who purchase the Ultimate Edition will gain early access on September 28. Read more about the game here.