I made an FPS that runs on 1980s hardware and you can get onto any surface you can see over. You just walk. Halo 4 or whatever introduced “mantling” and it was like, oh, why didn’t everybody think of this? Its absence now highlights any game with unimpressive obstacles. Even the Half-Life machina series Freeman’s Mind highlights how Gordon should be able to chin-up over some ledges and skip whole chapters.
Another example specific to Half-Life: the PS2 version’s long-jump module is a double jump. You just jump in midair and it fires off. No wonky crouch-then-jump command. Movement isn’t any less deep or complex. It’s just simplified to the point you can do it by pushing a button twice instead of playing piano.