If you're reading this wondering if you should buy it, listen up. Unless you see somewhere that they have completed the migration from Games for Windows Live (GFWL) do NOT get it. Due to GFWL not functioning for D3 currently, starting a new game (or if like me you migrated computers and needed a fresh install) means you can't save any progress - not even in the single player mode. :(
That said... I loved DiRT 2, and was very excited about getting DiRT 3. While D3 has its own charms, it's not quite as engrossing as I found D2, though it is extremely pretty and sounds great. If you were head over heels for D2, you'll at least have a close platonic relationship with D3.
TL;DR: Good game, but not right now.
Edit: I did get D3 to save profiles after uninstalled GFWL, downloading a new client and manually re-installing it, as even using a local GFWL profile refused to work. I still don't recommend the game until Codemasters decides to bother properly updating it.
A few people bizarrely accused me of making up this issue, but simply going to the Community Hub for this game shows there are a LOT of people having this exact problem, and Codemasters have now taken over 6 months since announcing they'll update the game to fix this, but have not.