Anyone expecting any kind of arcade racer will be incredibly disappointed. Project CARS is incredibly realistic, and anyone who isn't a hardcore racing fan will probably hate it, or complain about the actual "difficulty" of it compared to something like Forza and such.
EDIT: To further my opinion, I just put an hour or so into the game, finished a 6 race kart championship, and I have to say I'm quite pleased with the game so far. Good driving physics, the game lets you start off wherever you want so if you want to start slow and go for something like kart racing or just jump into serious racing and such you can. Learning curve takes a moment to get used to, and since I still need to switch over to an actual racing wheel I'm sure I'll need to doubly work on my skills, I think it won't be too hard for someone who really enjoys realistic racing games to get into.