I used to be much more of an ecclectic gamer back in the day. Then the MMORPG came out and I began to slack on my library. I've spent thousands of hours on all the MMORPGs I've played up to this day. I don't regret it though. I absolutely love MMORPGs.
My favorite part of them is the exploration involved. Sometimes the most fun you'll have is exploring the huge world at your leisure, entering a weird dungeon and seeing all these powerful enemies. It's like the ideal Zelda game that never was, and never will be.
Edit:Oh wait a minute, Zelda 1 was pretty damn close to the MMORPG feel. You could explore all you wanted, and enter grossly overconned dungeons before you were supposed to.
Let me rephrase my previous statement: The exploration and design of the MMORPG is like the ideal Zelda game that will never again be.