Assetto Corsa is, for the moment, not a bad, but not especially a good one too. The development of the game is really long, the content quite poor.
Graphisms are really good, not too say impressive, interior views are good. The driving sensation is good, you feel the difference between the cars, and some of the ones proposed are quite challenging to drive.
But, once again, the damages (to date 15/10/2014) are ridiculously made. No physical damages (so you can't cheat on that point), mechanical damages wrongly done, the only one you can feel is when you down shift too fast, it breaks the engine, so you can't continue your lap...
The penalty system when you leave the track is idiotic (you have speed down to 50 km/h or wait 5 seconds !), would be better to make thinks real by make the outside of the track dangerous and gravels impossible to drive fast in.
To sum up : buy it only if you're waiting for another car game or if you don't really what to do, if you are a sim fan, could be interesting but not necessary great, if you are just a gamer, better car game exists or will be released.