Morrowind, because it’s just modern enough to have a reasonable control scheme and proper 3D graphics, but old enough not to be dumbed-down for consoles in terms of game mechanics (magic effects and whatnot). Plus, it has by far the most interesting and unusual setting (compare netches to the normal animals you find in Oblivion and Skyrim) and also a fast-travel system that’s actually integrated into the setting in a realistic way.

I do wish the non-magic combat were a little more Skyrim-like with power attacks and finishing moves and whatnot, but lack of that is a small price to pay to gain the above.

I feel like Daggerfall, by reputation, might be even more interesting in terms of the scope of stuff you can do (e.g. climbing ladders), but the graphics and control scheme are just too primitive and I find it hard to get into.