I find this topic to be kind of unfair, being that there are games WITH an ending and there are games WITHOUT an ending. For instance, someone can play an online game for 100 hours and its nothing, or a non-ending game like Animal Crossing, but a game with an ending, spending 100 hours is like...WOW, you spent THAT long on it! So there should really be 2 categories.
Longest time spent on a game with an ending : 125 hours on Pokemon Blue back in the day, got ALL 151 pokemon! Wow...that was like, 6 years ago I think.
Logenst time spent on a game without an ending: Animal Crossing, not really sure but I played it daily for anywhere between 30 min to 2 hour streaches for about 3-4 months.
And I find more pleasure in putting the time in Pokemon than in Animal Crossing.