Greyhawk: I like it--including the stuff after the Greyhawk Wars. I've run Greyhawk Campaigns throughout most of my 20 year history as a DM. The only thing better would be a homebrew campaign setting.
Jedisoth said:
Forgotten Realms: This is the only one for which I have an actual Love/Hate relationship. I loved the first incarnation of the setting. I hated how it became bloated by its own canon and how the über-powerful NPCs were show-stealers from those who should have been the real heroes: the PCs. (Yes, I know that a good DM avoids this, but all I ever hear about is Drizzt this, Elminster that, the Symbul the other. If they're ALL THAT, what's the point of the PCs? To save Village Doesn't-Matter-to-Elminster from hungry goblins, eh? B-O-O-RING!)
I really wasn't all that familiar with the first incarnation, but I agree with Jedisoth. Many people I've encountered over the years also wanted to mimic these characters. ("I wanna play a dark elf ranger with two swords" and "I wanna play Elminister's nephew.")
I lump in Kara-Tur and Maztica with the Forgotten Realms because of their unoriginality (Forgotten Realms has a lot of that). And I agree with Jedisoth--Al-Qadim should have gotten its own treatment, separate from the Realms.
I also get the notion (from Dragon Mag articles I've read and elsewhere) that FR were developed so quickly to screw over Gygax. Not a fan of that either (but that is topic for another thread).
Dragonlance: I liked Dragonlance when I was growing up. Not a fan of th 5th Age stuff.
Planescape: Hands down one of my favorite settings. The only drawback is trying to convince others to play. ("Yeah, its a game where you character takes a philisophical attitude toward the multiverse." "Oh...I rather play Greyhawk.")
Dark Sun: I liked Dark Sun. Everything was overpowered. Should be perfect for 4e...or the worse setting for it. (Nobody likes to keep track of water rations).
Spelljammer: Meh.
Ravenloft: I like the concepts of this setting (Fear/Horror/Madness/Investigation) but not the idea of being inside a prison realm. The original Ravenloft module was great--even though it took awhile to get to the castle.
Birthright: Never played it. Only glanced at the books. I am Switzerland.
Mystara/Known World/Hollow World/Red Steel/etc. Maybe this world would have stuck out better in my mind if it had been AD&D. But since it was mostly made for D&D, I didn't pay much attention to it. Some cool concepts, but I'm not conversant enough to have much of an opinion.
Eberron I honestly forgot all about Eberron until I read this thread. I was never really sure what to think of it. I remember glancing through the rulebooks when they first came out thinking to myself: "Why would I want to invest in
another setting that could end up being a fad and forgotten in a few years?"