The AI is pretty good I have to say. Lots of satisfying races. The physics are very forgiving in that you can beat and bang and your race isn't over. NR2003 doesn't have much slack in you rubbing the car ahead in a turn and you spinning.
My problem is with car handling in general. Wish it was easier to setup cars, that menu is a nightmare. Just give me simple instructions on what to change. There is a Google Docs guide to car setup where it asks "tight in and loose out? do this..." and so on. Why not have something like that with a guided engineer, like the Moto GP series
FFB on the Heat series isn't great either. Really noticeable on road courses. It does the job on ovals. What Heat does well is provide an offline experience with an actual career mode. Its not realistic and gets a bit "grindy", but its not arcadey, you don't need to win all races or get medals or anything. Meet sponsors expectations and you get cash.
One standout is the dirt racing on NH5. It feels very wonky when you get on track for the first few laps, but once you get in the groove, it feels great. Hidden gem of this game. My pro tip: run two careers, one on really hard in the dirt series so you can work your way up, and one in Cup where you build up a team. Don't bother with Trucks or Xfinity.