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.
I’ve quite recently made run of D2 up to middle of Act V and rhen lost interest at all. It was a bit grindy, but the main problem was convenience factor. I was at the point when my summoning Druid started to lack behind and it is pretty much impossible to respec skills to fight that sort of bad decisions… When I was a teenager I’d just scratch it and start over with better build, but ain’t nobody got time for that now!