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.
For me it would probably be most old DOS era games like Dune 2, Ultima Underworld, Warcraft 1, Civilization 1, etc. All of them were great, but it’s really difficult to get used to those old control schemes nowadays. Pixelated graphics wouldn’t bother me, but those like 15 FPS at max is also hard to get over these days.
Other than that it would be some newer games that lacks a bit of convenience stuff. Like e.g. Diablo 1, where you can’t run yet. Or some of the first 3D accelerated shooters that can’t remap controls to WASD.
Having to rely on reading and retaining information in manuals is a big thing that keeps me away from a lot of DOS games
And don’t even get me started on that damn copy protection level “what is 7th word on 16th line on page 23 in manual”!