An interesting thing is I think a lot of it's caused purely by the graphical fidelity. For instance an animated character back then was just a key framed polygon soup - compare that with the convincing humanoids games have now.

And yet often the actual gameplay code itself may only be 2x to 3x more complicated then the days of old.

I think of counterstrike for instance - it's still just guys shooting guns in a constrained arena.