I want to find a fun MMORPG to play when I want a timesink. I haven't played any in a long, long, long time so I don't know what is popular anymore. I am playing a bit of ESO right now which is fun, but it is mind numbingly easy so I'm losing interest.

What should I try? I guess it can be an old one as well. Or maybe I should just find another genre to play...

Well, feel free to suggest me any titles.