You asked your initial question to me on another thread (apologies, I was out at the time and didn't get the chance to respond) and
@GOTMAXPOWER sums it up well.
DiRT Rally for me just feels tidy and neat from the moment you turn it on, I didn't actually get the chance to fully purchase SLR but from the demo it just had a lot of technical kinks and small issues like an average co-driver and limited visibility of what's ahead made me feel the game was holding me back.
DR on the other hand is just so refined and captured the feeling Colin McRae 2.0 hit years ago on PS1. It's fast, efficient and nothing really stands between you and the track aside from a half-arsed 'race team' mechanic. Daily, Weekly and Monthly events give you constant ways to improve your driving and test how good you actually are when you can't reset or choose what tracks or cars you want to drive - against 1000+ daily players each day.
The gameplay experience is just so fluid. I can understand why some might find it slightly boring (probably the same people who feel the same in some ways with AC) but I've not felt the feeling of satisfaction from pushing to the edge DR provides and the tracks are mostly great. Rallycross and Pikes Peak are satisfactory too.
It's slightly light on content, but everything here is tweaked and works as it should. To be honest, I expected the same from Assetto and perhaps I should have done a bit more research to see the current state of the game. Amazing sim, not so great overall game.