I thought a really interesting take was that in Metro 2033.
SPOILERS
So there's a whiny little kid, hunched over some dead body. He talks a lot. You agree to escort him. You pick him up and put him on your shoulders. He is no longer visible. He spots creatures (though to be fair, in quite a non-specific, unhelpful way) which are behind you, and this is good because in that section the monsters are ALWAYS behind you, and move very fast.
I guess technically it's not an escort mission, because he has no separate identity, but he does seem to change your aim a little bit (it feels heavier, and it glides more than when you dont have him on your back). He helps, and it is useful. It was handled well.
To be fair, that game is mostly made up of missions in which you are running with someone else, and for the most part they work fairly well, giving you an assigned role, and allowing you to get on with it. And the NPCs are invulnerable when they need to be, and all have automatic weapons. Yeah.