Psion said:
More generally, let me add that all campaigns need
- A driving conflict(s) that can be used as a common source for adventure ideas and plot development. (IMO, lacking this is what killed spelljammer.)
- A default activity/model for PC groups.
Well, they didn't go far enough with it, but I felt the whole elven/orcish cold war was a very compelling driving conflict. Especially the fact that it made groundpounder (and really any non-elvish/orcish) PCs feel like a tiny and insignificant part of a massive whole... yet left room for them to make a difference.
What killed Spelljammer was Planescape.

And the lack of any kind of consistency in its novel line.
Anyway...
I like a strong - very strong - techno-fantasy element. Space sorcery, modern magic, cyberelfpunk... it's all good, but steampunk is my personal favorite. I'd rather lose the fantasy element than the sci-fi element.
Spelljammer, although like Eberron lacking any real tech, went way further out in creating its own interlocking web of magical 'sciences,' like the various types of helms developed by the different races and the elven and orcish 'biotechnology.'
Today, Mongoose's superb OGL Steampunk wins hands-down for this sort of thing, IMO, although the Iron Kingdoms, Dragonmech and the now sadly defunct Dragonstar have more concrete flavor. The OGL Steampunk mechanics and toolkit approach suit my present needs best, although all of those products (and, for all its awful mechanics, BESM d20 and its superior kin, Mecha d20) have been handy.
I like a darker, dare I say edgier, world. More Dune than Lord of the Rings, more Xenogears than Shining Force, more The Matrix than Star Wars.
Iron Kingdoms handles this to my satisfaction. Midnight and Ravenloft, although cool in this way, are less my style.
I like extremely competent PCs doing extremely cool things. But I also want extremely competent NPCs (enemies and allies) doing other cool things. If PCs can get to low-mid Epic levels (and they can, when I DM), so can NPCs. I suppose it's borderline 'superheroic,' but I like the end result and the way it plays out. Those things don't have to be overt, though - a superbly deft, suave infiltrator who can think and talk his way through anything is as appropriate, or moreso, than a hulking fighter who can cleave his way through an army.
Actually, from what I've seen, White Wolf's Exalted would be a good fit for my preferences in this. But high-level d20 works just fine.
I don't neccessarily like low-magic, but I strongly prefer low-spellcasting. That's a game mechanical preference - I hate dealing with D&D spells. Incantations, rituals and custom magic items are fine, although I also don't like the standard magic item treasures.
I like the incantations system. The magic systems of Conan, OGL Steampunk and Grim Tales all seem like possible alternatives. I actually prefer standard d20 psionics to their magical equivalents - fewer powers, greater control.
I like an unusual or offbeat villainous group - could be aberrations, could be intelligent, organized orcs, could be a particular type of humans. I don't like the standard D&D outsiders, good or bad, and I'm sick of the typical antagonistic races (stupid orcs, drow, yuan-ti, githyanki).
Eberron really soars in this regard; the Daelkyr are very cool, Rakshasas have always been faves, and the other potential villains have a lot of potential. Iron Kingdoms also does a solid job.