What makes a great Campaign setting?

I have happily been running my current Greyhawk campaign for the last four years, and hope to do so for the foreseeable future.

However, I've become interested in Eberron, and doing so has made me aware of what really "sells" a campaign setting.

One thing I can assure you it's not: It is not the core campaign setting book! No, I find the ECS to be rather dull. I prefer reading other sorts of game books. (Complete Warrior makes me very happy. Go figure).

No, instead there are two elements that can make a campaign setting stand out and really make me want to play it:

* Novels
* Adventures

Looking down the list of campaign settings I find interesting (and have run games in), I find the following:

The World of Greyhawk - the granddaddy of settings, the WoG is rather unprepossessing with respect to its core books. However, when it originally was created, it had great adventures. Vault of the Drow? White Plume Mountain? The Slavers? Very, very cool.

Greyhawk never had a coherent novel line - I have Gygax's Gord books, but they're minor and late compared to the setting.

Forgotten Realms - Back when the FR came out, TSR was producing some rather substandard adventures. On the other hand, it coincided with TSR's discovery of some good authors. The FR novel line has always been one of its stronger points; and some of the early novels (especially Azure Bonds) were very evocative. So, the FR interested me, and I ran a campaign there for two years.

Unfortunately, then The Horde and Maztica came out, and TSR lost their way with the setting. :(

Dragonlance - This is a world built on the novels. It also has some fine (and not so fine) modules in the original series. Unfortunately, I don't like the world beyond the original storyline that much... but for a while, I was rapt and very interested in the setting.

Eberron - As I said, the main campaign book doesn't interest me that much, but the adventures (Shadows of the Last War, Whisper of the Vampire's Blade) are fantastic. Well, they are to read. I'll be very interested to see how they play, sometime in the near future.

The other thing which has helped "sell" Eberron to me is the short story included in the first adventure module - I love that story. Very evocative and makes me fascinated by the setting.

As for non-TSR/Wizards settings: I haven't been looking for them so much over the past few years. Maybe other people can chime in.