mystral: So, if you've played all those, how can you say they're a "repetitive grindfest"?
I don't know about Star Trek Online or DC Online, but WoW and TOR only have about as much combat as single player RPGs, and you can easily level to cap and finish the story by just doing quests. You never have to grind anything if you don't feel like it, until endgame anway.
Breja: Because they are. Every damn quest in WOW is exactly the same. Every quest in TOR plays exactly the same. And the combat is about as dynamic and diverse as my social life.
And that's different from most singleplayer RPGs how exactly? At its most basic, almost all RPGs have the exact same quest (i.e. go there, kill/fetch something, kill everything in the way) over and over.
I won't argue over the combat since I hate WoW-style combat too, but apparently people like it.
That being said, if you don't like the way WoW plays, maybe you should try something else instead of painting all MMOs with the same brush.
The Secret World, for instance, has investigation missions in which you (usually) don't kill anything. Instead, they're more like a mini-adventure game where you have to solve puzzles to progress.
Or Dungeons and Dragons Online, all quests are instanced dungeons (some of which are among the best level designs I've seen in RPGs) where killing stuff gives no xp unless it's a bonus boss. In fact you get bonus xp at the end if you can finish the dungeon while killing as few enemies as possible (it's based on D&D 3.5, so sneaking is just a matter of maxing 2 skills and being smart and patient).
The point is, MMOs are very varied in their approach once you get past all the WoW clones and try the more niche ones. I'm pretty sure anyone can find one they would enjoy, if they just take the time to find it.