For my money, Guild Wars is the best "MMO" out there. It's almost as if the lack of a sub meant the game could be, to a point, streamlined. It never felt like a grind because, in reality, it wasn't a grind. You went through 3 campaigns, your character maxed at a naturally achievable level 20, and the PvP endgame where MMOs usually slip up... was actually brilliant.
You could then go back through the campaigns to find special side missions and earn further XP bonuses and other goodies for use in the constantly expanding PvP mode and, unlike other MMOs, the limited slots available to players meant combat was always balanced. There are no mods to extend the hot key options; just a selection of what... 6 slots? Or was it 8? Can't remember.
It's still going strong. I still play it from time to time.Eurogamer has Epic Preview