

Part of it is about how close you are to the target FPS. They likely made the old N64 games to run somewhere around 24 FPS since that was an extremely common “frame rate” for CRT TVs common at the time. Therefore, the animations of, well, basically everything that moves in the game can be tuned to that frame rate. It would probably look like jank crap if they made the animations have 120 frames for 1 second of animation, but they didn’t.
On to Fallout 4… Oh boy. Bethesda jank. Creation engine game speed is tied to frame rate. They had several problems with the launch of Fallout76 because if you had a really powerful computer and unlocked your frame rate, you would be moving 2-3 times faster than you should have been. It’s a funny little thing to do in a single-player game, but absolutely devastating in a multi-player game. So, if your machine is chugging a bit and the frame rate slows down, it isn’t just your visual rate of new images appearing that is slowing down, it’s the speed at which the entire game does stuff that slowed down. It feels bad.
And also, as others have said, frame time, dropped frames, and how stable the frame rate is makes a huge difference too in how it “feels”.
Out of curiosity, did you have an actual N64 hooked up to a modern TV? A lot of those old games meant to be played on a CRT will look like absolute dog shit on a modern LCD panel. Text is harder to read, it is harder to tell what a shape is supposed to be, it’s really bad.