I played it for about 30mins this morning before heading into work.
Set it to expert but with ABS on and cosmetic damage. I drove the Audi and Porchse.
The thing that really struck me here was the AI. Holy shit, it's good. On my 2nd lap in the Audi, I was driving drafting the AI past the start finish and into the first right hander. I got inside but got a little sideways and into the grass a little and lost some speed. The AI shot right up besides me. We went through the following esses side by side. There no was contact and no AI having the "get back on the racing line ASAP!" mentality. The AI completely adapted to new situation like you'd expect a good racing driver to. I was able to pass the AI by outbraking myself a little and then cutting his front end off on turn in. Even then, instead of ramming me, the AI actually checked up and tried to switch to an outside side and was underneath me again but I had enough power to stay ahead.
Another time, I had 3 AI cars in front battling. One got underneath another and got by while pushing out the car that's being passed. The 3rd car in line tried to shoot the gap also and ended up making contact. This pushed both cars and then I tried to get by both of them. I went for it and got in hot and scrubbed off too much speed mid corner. The 2nd cars by this time had recovered and used it's momentum to re pass me on the outside.
Driving in career mode is going to be a lot of fun.