The track is amazing. It looks great, it's an amazing drive, even without the Sudschleife, I love it.
The one problem that I've run into, in multiple cars now, both Kunos and modded, is that the bottom of the second hill at the end of Döttinger Höhe seems to send the cars bouncing. The Kunos GT40 hadn't even finished bouncing by the time I cleared the hill, and I went over the crest with the car pointed downwards in mid air.
I don't know what causes this, but I hope it's able to be fixed.