I have never stopped playing in Greyhawk, per se. I have taken breaks and tried FR and most of the TSR settings, and most recently Ebberon, but I've always returned to Greyhawk.
I can understand why some might have given up on Greyhawk, however. It radically changed its tone once with From the Ashes and then had two abortive restarts with The Adventure Begins and the Living Greyhawk Gaz, which was never followed up. More importantly, I think, Greyhawk has been hurt by being so confined to just the Flanaess for so long. Its like a pot of water being boiled since the early 1980's - eventually the water turns to steam and boils away.
People who call Greyhawk generic are certainly entitled to their opinion but I think such comments reveal as much about the person who finds Greyhawk generic as they reveal about the setting. Greyhawk is, IMO, the ultimate DM's toolbox setting, but like a toolbox it doesn't do much by itself. You have to use the tools. If you don't, won't or can't, Greyhawk will just sit there and seem "generic." What you bring to Greyhawk is as important, if not more important, than what Greyhawk presents to you straight out of the box. This is Greyhawk's genius, if I can use that term, and its burden. Greyhawk is not ready to rock right out of the box - it has to be assembled. You are up for that or capable of that or you are not. The experience of those who are not is that Greyhawk is "generic." In this, Greyhawk is very much old school as compared to more recent settings that come with plots and hooks you can hardly avoid and which as a DM you must either work with, ignore or work around. That's not a value judgment, by the way. It just a different way of presenting material with differing expections for how that material will be utilized.
YMMV.