Years after Fallout and Fallout 2 came into being I had replayed the first one over 10 times.  The second, several times, though not so many only because it is much longer and more in-depth.  This series was so great because of the simple fact that it is doubtlessly the least linear game I've ever met.  There were so many quests to complete, and each outcome small or large created repercussions throughout the game.  It was hilarious but at the same time one of the most violent things at the time (though hardly even close by todays violent standards).  The violence was fun, interactions with various characters you meet were fun, the satire of just about everything from scientology (even Tom Cruise and Nicole Kidman) to karate flicks to sci-fi greats, with even nods to more recent pop culture like South Park.  The breadth of the game still astounds me.