I was trying a few different cars in the 0.3 open beta, all on the Red Bull Ring GP track. The difficulty of beating the AI, and the AI behaviour, are very car dependent. The trackday Dallara Stradale and the M4 GT3 Evo are fantastic fun to drive (both have slicks), but I found the AIs could in places push the nose of their car against the rear of my car and spin me out. Even on 80-100% difficulty, once I got into 1st place, I was much faster than the AIs.
The M4 GT3 Evo felt amazing to drive, less sterile than ACC's GT3 cars. The Dallara is also amazing to drive, but the cars have individual identities, which is good.
What I did have, using a controller, and I think I had it with both the Dallara Stradale and the M4 GT3 Evo, was it felt too easy to get into an unrecoverable slide on certain corners. A particularly bad corner for it with the Dallara is the penultimate corner. Maybe I just need to get more used to the audio cues of approaching the amount of stick movement beyond which the car will slide. I've never played any other driving game where you have to find an exact amount of stick movement to take corners like this, I don't know if it's intentional or not, it certainly makes it tricky to take corners as fast as possible while never going into an unrecoverable slide.
I felt the previous version wasn't very sim at all, far too much fake difficulty, but 0.3 feels a lot more realistic to me. I can see myself running it up just for the fun of racing against the AI, whereas with the previous version I just thought "okay, I'll wait for the next version".