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.
Outer Wilds. Wish I could forget it, as the progression is based entirely on player knowledge it has 0 replayability(I mean this as an endorsement).
Watch playthroughs on YouTube and you get to see someone else play it for the first time.
I’ve recently started using the archipelago randomizer mod to get another taste of replaying it, but unfortunately the satisfaction of completing a rando pales in comparison to that first experience.
I will never not recommend this game. It’s so good and I can’t wait to see what Mobius comes up with next.