I don't like any MMORPG that much. None of them are skill based. They're all experience points/grinding-at-all-hours-of-the-day based. Although, there is this new MMO coming out called Darkfall that is, in fact skill based. I think that'll set a trend.
One thing that has never been done before is an MMO that is entirely luck based, like Toribash.
I don't know how that would work though. Maybe some kind of Rock, Paper, Scissors based fighting system, or something.