Forza Horizon is more geared towards street racing, whereas Forza 4 is more geared towards actual racing, the cars which can be driven in this game you may see on actual streets. So in essence the two games are modeled quite different.
Forza Horizon on the xbox 360 takes gamers into the next level of racing, there is a huge transition between this title and the previous release Forza 4. The gameplay is superb and really sharp, the contract and the streets are real streets, and this is a massive improvement on the previous releases.
There are also game aspects presented in the game where if you hit barriers and various obstacles like posts and signs you actually get upgrades, which is a new spin on things. There are also speed cameras located within the game and as you drive through these it takes a snapshot of the actual speed at that given moment, this is turn can then be challenged by other players who try and beat the speed that was clocked at that moment.
The handling is also slightly different from the previous title Forza 4, the handling now enables a player to be able to regain control much easier which I feel has improved the overall experience within the game. The upgrade system on Forza Horizon is also very much lifted from the previous release, you get the same old Rim Style, Engine, Carburetor, I expected them to upgrade this to include new elements and choices but sadly this was not to be.
Another problem with the game which should have been addressed is the more top level cars, granted they have included many more cars than the previous games, however you only have certain options to upgrade certain cars, rather than adopting this model and applying it to all cars, I felt they should of gone that extra mile.
Overall the game is incredible and the attention to detail is superb, I love traveling to the Festivals and seeing all the rides and people that are about, also having the option to engage in various things, from spray painting your car, to races to other pleasures which adds to the overall experience and gameplay.
One of the things with the Xbox 360 is you also have the option to take it online, where here you can take it to the streets where you can compete and enter races with numerous online players. They have scoped it down a bit, now you get to race 8 players as opposed to 15, this was largely done I feel because 15 was simply to many cars to be racing against at any given moment. The cut back actually works better, as they say sometimes less is better.
I would say that Forza Horizon is more geared towards street racing, whereas Forza 4 is more geared towards actual racing, the cars which can be driven in this game you may see on actual streets. So in essence the two games are modeled quite different.