Morrowind! I had to actually think a bit during quests, whether that was picking up on clues for what would make a good gift for a certain NPC that is part of the main quest or following directions to get somewhere. Getting used to the different traveling systems was enjoyable as well. I really liked the twist on the chosen one trope, especially when you meet some of the others. And the ways things fit the prophecy. It’s so slow at first to get places on foot, but by the end you’re whizzing around in the air. Breaking through the power curve is fun to build towards. Modded Skyrim is pretty good, too, once you get rid of the gamey things like waypoints and the UI generally, put some decent quests in, justice for Parthanax, open cell cities, unlock spells, fixing the magic system, etc etc. But last time I touched something in my stack it all fell apart and I haven’t felt like putting the time in to getting it to a decent state for a few years.