Alrighty, let's give this a try...
Greyhawk - Love it. It's got such a deep background, without getting overburdened by canon, that it's phenomenal. It's been one of my favorites since the 1e days. I think it has probably the best setting map in the history of gaming settings, too - in both artistry and "cool" value. Yes, there's some silliness to the place names, but that's easy to look past. My favorite is the 1e-era box set, but the Gazetteer version is pretty okay, too. I'd prefer to ignore all the Greyhawk Wars stuff, personally. If I want relatively vanilla fantasy, and I don't want to homebrew, this is my fave.
Forgotten Realms - Which one?
Old Grey Box: Love it. Heck; I'll add in most of the FR series supplements.
2e Box: Meh. Avatar, schmavatar.
3e: Hate. This is what happens when the canon from an exhaustive fiction collection are allowed to drive a setting.
4e: Pretty okay. The map hurts my enthusiasm a lot, but the setting is actually pretty good.
Dragonlance - Hate it, mostly for the aforementioned joke races. Also, the 1e Dragonlance Adventures hardcover was a travesty.
Planescape - Meh. Unfamiliar with it, and it looks to suffer from the same canon overload as late-era FR.
Dark Sun - LOVE, but particularly the original box set. Sadly, it was thoroughly trashed by the novel line. The early supplements are pretty awesome, but the mechanics had some flaws in the original release. I'm looking forward to the 4e version; even if they mess with the setting, they can't do anything worse to it than TSR did!! And besides, I'll always have my box set for setting flavor.
Spelljammer - Like it okay. It was a fun idea, and a better implementation of it could be cool.
Ravenloft - Hate it. Conan Meets Count Dracula. No thanks; horror is best handled by a game system suited to it.
Eberron - Like it. May love it if I ever actually get to use it. I dig a pulp-style campaign.
Birthright - Shrug. Mostly ignored it.
Kara Tur - Double-shrug. Asian-themed adventuring is probably better done in L5R.
Al Qadim - I'm fond of it, but didn't get much into it. It was not the direction I was heading during the Great Setting Glut of 2e.
-O