@Ganymede Honestly, it is the people that have brought me back again and again. I've been doing this just as long as you, and I have taken sabbaticals which sometimes last a couple of years, but the thing that has always brought me back are the people. I have had some really great friendships develop from my time on these games. Even years later I talk to some of the people I have met.
Sadly, I've also lost track of many of the people I used to play with. Sometimes I end up finding them again on places like this, or randomly elsewhere. Hell, I even found one once at a RL Job...that was a surprise.
So, yeah, I have to second Ganymede's comments in regards to the people.