Well, Buddy Christ, as you can see, it's clearly a matter of opinion whether rFactor is worth it or not
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So I'll give you my opinion:
Mods and modability:
First of all, I agree with much that has been said here about the problems with mods and not having them. I personally always had troubles with games that were dependent on mods, simply because it takes a lot more effort and time to thoroughly enjoy them. I believe however, that if you're willing to dedicate that time to a sim, you might really have a lot of fun with it. Problem is of course, that you won't know if you're willing to do that before you've tried. That's a big problem, I don't have a solution for.
As was said before, installing mods is really as simple as it can be in rF, so no problems there. (Only sometimes installing a mod might mess up some files in your base install, which happened to me when installing the 1070 patch and Lienz. Was easily correected by dropping the original files in the appropriate folder, however).
Feel (Physics/FFB):
Again I agree with much that has been said about this. The default FFB settings of rF just didn't do it for me. I felt oddly detached from the road. But then I asked in the forum (major problem for me was that steering resistance didn't increase on turning in) and got quick help. I needed to change a setting in some .ini which I did. This really made FFB feel a lot better. However, I think that it should not be necessary to fiddle with some strange .ini-file in order to get decent settings. It wasn't much of a problem, though, but I think that something is not right when you have to do that.
As for physics, I can't really say if they're better, worse or just about as good in LFS. But what it comes down to for me is feel. And once i got used to the feel of rF I came to like it quite a bit.
gfx:
As much as I disliked the graphics of rF at first, I now like them. I'm running it on dx8 and I can't really agree when ppl say it's rubbish when you're not using the highest settings. I even like them a little better than LFS-graphics actually. It just looks a little more real to me. However, graphics are really not important to me. But this clearly is a matter of opinion. So you'll have to decide for yourself.
PCC:
Well, the PCC mod is probably one of the best mods available for rF atm. It looks great and the cars feel really good to me. Can't comment on realism, however, as I have never driven a Porsche Cup Car i real Life - but I think most ppl who comment on it haven't either.
Community:
I think the rF community is neither better not worse than the LFS-community. Might not be quite as big, but overall very helpful and, erm, just "normal". You do have some annoying fanboys just like here who will bash any other racing sim out there. But there are also, just like here, the voices of reason who try to shut those fanboys up (sometimes to no avail unfortunately). You will also find that the forum is rather strictly run, though, which I personally don't like. Warnings are handed out rather quickly, when you mention LFS as being superior to rF in any respect. Same goes vice versa, though. Posts considered flamebates will be removed in no time (as it recently happened when ppl said the rF Sauber looked much better than the LFS Sauber). So it will be almost impossible to have a conversation about the pros and cons of rF compared to another sim. So you have to be much more careful over there. That really puts me off, as I believe that a community should be allowed to take care of itself. But if you don't mind that, you'll be fine over there.
Did I forget anything? Don't know, but it doesn't matter, since noone will read my post in entirety anyway
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Edit: Of course I forgot something: AI. Naturally the rF AI is _way superior_ to the AI of LFS, and I use rF for offline play only (and therefore can't comment on netcode). And nothing beats the quick and easy pick-up-onlineplay LFS provides.