Out on the open road you'll pass civilian vehicles - apparently the E and F class cars of Forza 4 - and meet AI racers in supercars, cruising the state and waiting to be challenged. Without Test Drive Unlimited's massively multiplayer online racing you'll have to do without being called a twat by someone on the other side of the world, but Horizon's AI racers will respond to your challenges and are ready to race at any time.
In place of a true multiplayer world, you're always engaged in asynchronous online play with your friends and the entire world. Every road you drive will have its own leaderboard and every corner you drift around will be tracked by Horizon's own version of Forza 4's Rivals system. Head-to-head multiplayer will be demoed later, but expect Forza 4's sixteen-player racing to give way to eight-player races in Horizon. It's a big world to render and a big world to get lost in.
To navigate it, Horizon has an on-road GPS - cornering chevrons mapping the route to your destination - operable with an in-game map or Kinect voice control. Like a voice-activated GPS, you can tell Kinect your destination or just ask for a route to the next event and Horizon will take you there, offering braking lines on corners as well as the optimal route.
But Horizon's real difference is that - unless you fast travel or enter a key event - you'll never see a loading screen. For the first time this is a Forza where you're always in the action, always behind the wheel, and always on the road. With Forza 4's livery editor, tuning, massive front end and thirty-second loading times it's possible to spend as much time in the menus as it is on the track. The same isn't true for Horizon; in an odd twist, it's the first Forza about nothing other than the car and track.
Horizon is almost certainly designed to be Microsoft's off-year Forza - like Ubisoft's B-team Assassin's Creed games or Treyarch's even-year Call of Duties - but Playground haven't even attempted to mimic what Turn 10 do best. They've taken the maths and the models and built a game that does everything Forza Motorsport doesn't.