First off, I have to say I thoroughly enjoyed the previous games in the Dirt series. However this one, as Amazon's description of 3 stars says: "It's okay".
The gameplay itself is of a high standard, with the car handling seeming quite realistic. The sounds are great on track too, and it's difficult enough that there is a feeling of accomplishment when you drift around a turn nicely.
However, I would say that the experience of playing the game feels quite 'lonely'. In Dirt 2, there was a central hub, where you could go into your motorhome and move around a complex and decide what type of race to compete in. In Dirt 3, there's only a series of triangles representing different race types, and it just feels a bit sterile. Even though you are in theory working your way up through a series, there's no sense of higher standing or presence in the rally world. It's essentially "complete this triangle to see the next triangle". Combine this with the fact that rally is one car on the track at the time and it feels like racing in a bit of a ghost town.
Anyway, to summarise, the gameplay is decent but the sense of progress is poor. The multiplayer is good, but bear in mind now that the game has been out a long time and the chances of getting a race are declining quite rapidly!