It is a more arcadey bit of fun racing game that uses the forza physics engine but slightly tweaked to make for a more simple experience for new comers.
It was made by playground games, which employ a few people who worked on the "dirt" series, with Turn10 having direction over the game.
This is not forza 5. Turn 10 are making forza 5, they just wanted to try something different and give something for people to play while 5 is being made.
I personally think its good fun. With all assists turned off its not too arcade like. Plus thrashing around open roads weaving traffic in my 600+bhp RS200 is serious fun