I was a RBR addict for years and I still love it.
When I first tested DR with the Rally Cross cars I thought it was just fancy looking with console pysics. But when I tried the rally part of DR I found the handling to be totaly diffrent and way better.
Then I tried driving the Pikes Peak cars and thought WOW this is f.... awesome.
It sounds fantastic, looks fantastic and drives like RBR and the force feedback is awesome too, perhaps one of the best ever. ( iRacing and AC can learn a thing or two from the FF menu )
RBR is perhaps more hardcore, in the code, but I really don't care since I don't feel much difference when I'm driving. (The Pikes Peak cars that is.) Dirt Rally is the best thing since RBR and its damn close in the driving department and knocks it out of the park in graphics and sound. I love it.