2005 is WIP, and 2006 version will be done afterwards. I’m pretty sure they should be able to get all of the cars in there, too, as there have been quite a few done for rFactor, including the Megane cup car.
It does lack the variable weather. Controls aren’t bad if you do a bit of adjusting. I had problems with the force feedback working exactly wrong by default, but once I fixed that, it is pretty enjoyable to drive.
The biggest downside is the lack of real cars and tracks until you start adding mods. Quality of such mods varies widely, but the ratings system at rFactorcentral helps find the good stuff.
The only place you can get it is to download it. It’s a huge download, at about 650MB. The demo gets you two tracks and two cars. Unlock it and then the options are unlimited (you have to have the full version in order to use mods). If there is a DTM mod out or forthcoming, rFactorcentral would have it.