I played Forza for years, Forza 4 massively. I lost the love with 5 as they took out all the great cars, including the Z4M and then tried selling them back to you with DLC. They also removed a lot of the great tracks like the Ring and left others in which were not as popular but cost effective to scan in reality and produce in the game. Now they're selling those tracks back to you. They also removed the storefront and made the multiplayer too basic to configure with private races in F5.
If you've never really played Forza before I'd imagine you would love it. It is a stunning game but having grown up with Forza from the beginning I'm put off by how Turn 10 have basically raped the game for greed.
I'm hoping Project Cars, which comes out later next year takes the driving sim crown from Turn 10.