MoogleEmpMog said:
1. The Ptolemaic physics.
2. The blend of fantasy and space, and non-traditional fantasy in general.
3. Stepping on the toes of other settings.
The first two in particular have proven highly effective barometers for finding people with whom I'm going to butt heads about *any* setting; what they want out of fantasy is diametrically opposed to what I want.
I've also found that to be the case. I've always liked Spelljammer, though I didn't play in it very much. There are some things about it, in retrospect, that could have been done a lot better, and I completely respect people who decide it isn't their cup of tea.
As for "stepping on the toes of other settings," though, that's a complaint that makes my ears rattle and my eyeballs roll out my nostrils. Defending the "purity" of a D&D world isn't about personal taste, it's just geekery for geekery's sake (something I've been very guilty of in past threads, so I'm throwing houses at glass rocks here, just so you know I know where I stand).
If any of the other settings had had meticulously detailed outer spatial regions that Spelljammer contradicted, it might have had some merit, but
really, sometimes nerdity becomes so odious that I've got to open a window.
There was a Spelljammer in Greyhawk Ruins. Well, yeah, there's a freaking Alice in Wonderland demiplane there, too, exactly how is a flying boat a deal-breaker? How is the setting that hosted
Expedition to the Barrier Peaks damaged in any way by a tacit acknowledgment that somewhere illithids and mercanes have managed to build spaceships of their own? Greyhawk and the Forgotten Realms are, have always been, exactly as pure as the English language, which is to say as pure as a bathtub full of mud mixed with equal parts maple syrup and Guacamole - they're both pastiches drawn from all sorts of influences, cobbled together from modules and supplements reflecting a wide variety of minds and needs. Look at Faerun's pantheon, with Finnish gods butting heads with Celtic, Norse, Greek, and one that looks suspiciously like he came from Nehwon, its names cribbed from Tolkien and C.S. Lewis, and that's all before TSR bought the setting and spliced in the Moonshaes, Vaasa, Maztica, Zakhara, and Kara-Tur. Or look at Oerth's versions of King Kong, Lewis Carroll's books, the crashed spaceship, the Central Americans, or the quasideity who dresses like a fugitive from the Boot Hill RPG, or things like the Machine of Lum the Mad, the Mighty Servant of Leuk-o, and the Apparatus of Kwalish. I'm sure it's technically
possible for game designers to come up with something that truly clashes with either settings' themes, but flying boats do not do it by a long shot.
The Forgotten Realms and Greyhawk have always been attached to myriad other worlds. It's part of what defines both settings. Oerth even has a god of space travel, Celestian. Spelljammers actually fit the genre much better than a lot of the things Oerth hosts.
Dragonlance fans have a better argument, since at least some of its designers (Tracy Hickman, but not Jeff Grubb) apparently always wanted it to be its own thing. Still, Spelljammer has so many tinker gnomes in it, Dragonlance arguably fits with Spelljammer even better than the other two, and no wonder - Jeff Grubb designed Spelljammer with Dragonlance in mind. Perhaps if he hadn't put so much Dragonlance in it, people would have liked Spelljammer better, but that's an entirely different complaint.