I owned rFactor for 8 months and tried hard to appreciate it. In the end, I gave up on it and gave the license away.
The graphics in rFactor are pretty good, especially the amount of detail in several of the ISI-created tracks. However, all that eye-candy comes at a cost: you need a powerful system to run it at decent framerates. In LFS, I generally get 100-120 fps running at full detail, 1280x960x32, 4xAA and 8xAF. In rFactor, I had to scale the in-game graphics settings back and turn down AA and AF to get 30-35 fps. If the framerate is any lower, the game and controller response becomes so laggy that it's more or less unplayable.
Physics are hard to judge. It seems very good in places and yet things like controller lag, mediocre and canned force feedback, limited steering lock, steering ratios and so on get in the way.
User-created mods are largely a waste of time. Even 8 months after release, there are only a handful of good quality mods.
But what really killed it for me was multiplayer. Trying to find an online game was an exercise in frustration. There are so many different versions of the various car and track mods that even finding a server that I was able to join without getting a version mismatch error was a hit and miss affair.
So, I gave up.