I have only played WFRP 3rd edition, not the earlier two (owned 2nd, did not own 1st but have read), so can't really give an unbiased "having played, here is my opinion".
The setting is of course what I love most of all with the general theme of "this is not a teenage power fantasy" (forget images of heroic figures with finely chiseled features saving maidens) and the earliest edition's admonishment onwards of "talking to the gate guard might more useful than killing a goblin" (I'm paraphrasing the original).
Most of all, the theme that "WFRP is where a player thinks they're playing some different version of D&D but really is playing a different version of Call of Cthulhu" (you really don't want to know the truth of things).
I quite love the 3rd edition RPG despite many nay-sayers. Far from being "board game", it's use of card-based-information decreases need to consult rules during play. Its dice system builds in some "indie-RPG" thinking that has gone on over the years without belaboring it (e.g., instead of success-fail, with extended versions of each, there is a whole other axis of potential outcome each time reflecting "success fantastically but still screw up somehow" or "fail but still come up with something" etc. possibilities). I wrote the review of WFRP3 in the last edition of Warpstone magazine so won't belabor points more.
That said you can find passionate fans of any of the 3 edition of the RPG who will advise "their's is best".
Oh, I also don't want to give GW money. I admit, may perhaps buy some skinks, but don't feel they have "respected the fan base". Even if they wanted to offer a "new version skirmish game" or whatever, they didn't need to ruin the setting to do so.