The first game that comes to mind for me is Civilizations 4. I’ve probably spent hundreds of hours playing but after getting used to 5 and 6 I have a really hard time going back. Going back and forth between 5 and 6 I need to rethink some strategies but with 4 I feel like I need to rethink everything. I don’t know if it’s because of the tech tree layout in combination with the civics system, things like unit stacking, or maybe just a bunch of little things but it takes me a while to readjust.
Diablo 2 - I’ve played all classes, some in higher difficulties, again and again and it didn’t get old for a very long time. Today I’m not enjoying these kind of games anymore but I’m not sure why. Are they so different or has my taste changed so much?