Well, i'm no MMO veteran having only played RO and City of Heroes. And enough people pointed out RO's good points and nobody but me seems to have played CoH so here goes:

* Character customization: Seriously, you could make your hero/villain look however you wanted it to. Hell a friend of mine built Cloud there with the new ´Giant weapons´ power pack. It was hilarious.

* Level synching: The Exemplaring/Sidekicking system was pretty awesome, let you party with your friends regardless of their level, did not make levelling meaningless as it still locks you out of powers if you're naturally low-level and when you're exemplared (your level is reduced to match the partners) and kept the rewards level-adjusted, so if you were sidekicked (raised level to match your friends) you'd still earn rewards normal for your level.