It's fascinating the different way people to respond to different racing games. I think a lot of it has to do with what you are accustomed to.
I am currently switching between GTS, PCars2 & AC (on the PS4). I have a lot more time in AC. GTS is just very disappointing. In the old, familiar mould, the game is beautiful to look at, has a sophisticated & elegant interface, graphics are fantastic - especially replays - but physics are not convincing & the FFB really bland. And let's just not talk about the AI!
PCars2 has taken me a lot of time to adjust to. The physics & FFB seem pretty detailed & challenging, but very "quirky". The AI is very good. The depth of content is pretty amazing & so are the TOD & weather options.
AC's physics & FFB are in a class of their own. Detailed, intuitive & impressively visceral. The cars sounds are also very impressive - they make GTS & PCars2 seem very contrived in comparison. This makes more of a difference than you might think to the driving experience. AI is pretty good - it provides you with a challenging race, even if the interaction with the AI cars is not quite as complex as in PCars2. Graphics are nice IMO - not nearly as "realistic" as GTSport & without all the options that PCars2 offers. However, AC is crisp & clear which makes the driving experience perfectly fine. The depth of content is lacking, no dynamic weather or TOD & the menus, replays & career mode are pretty primitive. However, overall the driving experience is far superior to GTSport or PCars2.