I have to say Final Fantasy. Man I never seen people so stuck in the past then the FF fanbase. They either love the 1-6 seires and hate the rest, love 7-9 and say the 10th killed the seires, You get the point they can't accept change.Don't even get me started on the Soinc fanbase.
Mines has to be Kingdom Hearts 1 and 2. Does two are the first games I ever spent the most time on. Whenever I got home from school I would play Kingdom Hearts. I looked up cheats, ask friends, etc. Then when KH2 came out I was joyed. I spent damn near 3 weeks playing that game. ah the good times. Aslo super Mario world.