You can talk OD&D versus AD&D all you want but when it comes time to compare campaign settings there is no discussion. The GAZ series set the bar so high I am not sure it has ever even been seen again by any of the competition. TSR tried to replicate this with the FR line but it was not nearly as well done. These continue to be scarfed up when you can find them. There are some that I lost and had to pay dearly to replace. If you get a chance to check them out and want to see a campaign setting done right you won't be disappointed.