My guess is that most old school-ish gamers hold these in pretty high esteem:
For all the hours I spent pouring over these and books from the 1983 boxed set, we never really did a whole lot in Greyhawk. I always had grand plans to start up a continent-spanning campaign of some sort or other, but it never materialized. Several characters we played lived in Greyhawk, but other than names on a map and places or origin, none of the world really seeped into our games. A few modules here and there made use of the setting, but even then I was more likely to place things in my own campaign world than use them as written.
For all the advantages I believe using your own world has, I do regret not making more use of the Greyhawk. My maps are still rolled in a tube somewhere in the basement, and the Glossography and Guide Book are still in the box along with photocopies of some map sections I planned to make use of but never did.
Jeff’s Gameblog recently had a great post on the script used in the maps, so check it out if you missed it.
Maps from here.