the things that makes MMO enjoyable for me are:
1. smooth game engine, I dislike cabals engine for example and I like smoothness of WoW's engine
2. nice party system with alot of dungeons and instances
3. good balanced pvp fights
4. alot of different armors and weapons, not like in RoM where you have only few different armors for each lvl
5. some innovative features, for example astral battles in Allods Online
and ofc nobody want's grinding, good luck with the game
