Ultima Online. Small shards made it easier for newbies to explore in peace, and it's easier to GMs to monitor player behavior.
It's also how I got hooked into animal taming (Those custom-color mustangs were a big seller).
I've seen enough of these small-scale MMORPGs to think that another one isn't needed, no matter how innovative. Personal opinion, of course, but I don't think it's worth much putting hundreds of hours in a purely conceptual game at this time.