Have you ever played a game that over some period of time you always went back to? Didn't matter if it was a video game, board game, card game, yard game (you know Hide and Seek, Lawn Darts), or sport, but you just kept going back to it. Maybe it is just me but for years on end I would some how get dragged back into to certain games and sometimes I just wondered back into it. In highschool I loved to play Stratego.
There you have it. I had that box at one point but now I own a simpler "Classic" box of the game. I would do my best to talk anyone that would listen into playing me. I still own a copy and it is sitting in my garage waiting to be pulled back out and played once again. Warhammer 40000 is another one of those games. I started playing it back in 7th grade (I had a copy of Rogue Trader!) and I am still playing today. I have a Blog Blast Markers. There has been many versions of the classic pen and paper role-playing games throughout the years and I always come back to your D20 D&D-esque games, currently it is Pathfinder (D&D 3.5+).
Though I think what has topped them all at this point is the Civilization series where i am sitting at over 700 hours with its current version. I have played every version of the game that has been released for PC as well as Revolution except Civ IV (though I do own a copy) and now they have told us that this Fall will see the next game in the series. Guess I am not getting away from this anytime soon.