Still a relative newcomer here , still finding my way round RQ and I can say the GW/Avalon Hill hardcovers have help in converting me out of a TSR/AD&D (1st and 2nd) 'splat book' never ending quest to get them all to play - when these books are self contained and a good 'journey starter' collection of rules - to build from and adapt.
RQ3 is pretty much my intro to Runequest specifically, with The Design Mechanisms own RQ6 getting me interested initially in D100 mechanics when it was originally released.