I was lucky enough to get my hands on a retail version of Dirt. And I have to admit, It's as good if not better than your expectations.
This game is sure to set a new benchmark for offroad racing games. The graphics are amazing, the sound is top notch, and the handling physics are nothing short of spectacular!
After my short time with it, i'll give it an 8.5/10 but once I get my own copy and put some serious time into it i am sure that score will creep over the 9.0/10 mark!
Buy it! It's well worth it!