It seems like there are several arguments put forth, some of which are matters of taste, and others which can stoke antagonism. I'll try to set them out:
1. I had a campaign that was "ruined". This certainly applies in a "well, if they were going to spend money producing something, I'd really rather be able to use it" sense, but I still don't see how anyone's bound to use any particular supplement in their games at home. If you're regularly bringing in new players and replacing old ones, and those new players have expectations about how Greyhawk is "supposed to be", I could see how this plays a larger role.
2. I didn't like the feel. Fair enough.
3. I don't like metaplots. Fair enough (and this relates to #1), though I think the arguments from the perspective of a gaming company, as presented by several posters here, are pretty compelling explanations for why they did it, if not justifications.
4. It was low quality. Fair enough.
5. It made it detailed, like the (dreaded) Forgotten Realms. Really? There's still a lot of detail left out of the FtA-era Greyhawk. I don't think DMs are restricted in their setting development generally, and certainly not specifically with FtA-era Greyhawk. This also carries with it the "you're a lazy DM" stigma (expressly stated, sometimes), which annoys people who liked FtA.
6. It's not Greyhawk. I find this one problematic. There's "I don't like it," and there's "it's not Greyhawk". In the latter case, you have to define "Greyhawk" in such a way that your statement isn't equivalent to "I don't like it." Nitescreed attempted to do so, and I think he succeeds in some areas, but creates a tradition out of thin air in others. I.e., your "tradition" has to be differentiated from your home campaign (see #1) or your personal conception of the game world. But to people who play in Greyhawks that don't resemble yours, "It's not Greyhawk" comes across as an awfully arrogant thing to say.