I'm assuming this is in regards to the TSR-created worlds.
I've read a little of all but the Eberron books. The Planescape books were wierd but interesting, the Greyhawk books seemed derivitave of the old Conan/Fafhrd and the Grey Mouser books, the Spelljammer books were just pirates in space, and as much as I love the Realms the books for both it and Krynn fall into the category of pulp (not necessarily bad, but prone to be cliche). The TSR books I loved the most personally have been the Christie Golden/James Lowder Ravenloft books, the Finder's Stone/Cormyr/Rise of the Archwizards Forgotten Realms books, and the War of Souls Dragonlance books... so as you can see, my opinion's a bit varied and includes the cliched pulp novels. On a side note, I hope Drizzt dies in a fire; he made my long-running campaign NPC Stareyes the mute good-aligned drow paladin (2E; I used to flub the rules of race/class combos on a regular basis) into something that people thought I was copying from that glory hog ranger.
Anyway, point being, I think all of the TSR/WotC novels have a great amount of room for improvement, and none of them are staggeringly original or intellectual (Planescape and Ravenloft come closest). But fantasy fans aren't picky, judging by what sold when I was working Borders and what my friends read, so they get exposed to a lot of stuff without even knowing there's a whole seperate use being made of the setting. Love it or leave it, it's highly likely that if you read fantasy you've stumbled on a TSR-created world at some point without even realizing it.
For the longest time, Dragonlance was the most visible TSR property... which even showed in their RPG sales strategy. The number of new Dragonlance books per year, not including continuous remakes of the War of the Lance, was second only to Greyhawk... which survived primarily based on being the first TSR setting (so it had nostalgia on its side). But then the Dragonlance novels began to decline on the NYTimes Bestseller list and in the sales figures, and between Spellfire and the Moonshae trilogy and the Drizzt books the Realms began to climb to prominence. This is why 2E became a bit Realms-focused, to be honest... the setting was the one selling at the time, and even though TSR's accounting department was crap, the marketing department knew which was their lead horse.
The licenses for the Realms still sell readily, when it comes to video games. Yes, there were games set on Krynn and even a failed attempt at a Spelljammer game. There was even the beloved-by-many-gamers Planescape game, Torment. But the focus is still on the Realms, with the old SSI gold box games leading into Baldur's Gate/Icewind Dale and their console appearances, which led into Neverwinter Nights, which is leading gods know where. Eberron's had it's shot, and hopefully it gets another attempt... it's not the setting's fault that DDO couldn't grip gamers like the juggernaut that is WoW. But for now, the non-tabletoppers more readily recognize the franchises that make up the marketing of Faerun more easily than they recognize any other.
The books still sell, the games have devoted followings, and that blasted drow has become the poster boy for unnecessarily powerful fantasy heroes in today's marketplace. For the time being, the Realms are firmly entrenched as the most prominently visible TSR/WotC world.