Dirt 3's weather effects are amazing, especially the rain. The snow tracks are really well done as well, as is the night tracks.
I prefer the racing progression in Dirt 3 also, and the fact that it has a wider array of car classes to choose from (

Group B).
The Gymkhana stuff seems to be really polarizing, but I think its amazing and can't imagine Dirt without it now.
As a sequel, it does feel like a sideways step from Dirt 2, sure. But if they build upon the stuff they established here, Dirt 4 should knock it out of the park.
Just make everything regarding the annoying 'advisors' optional and skippable, thanks.