Agreed with the post above. And you better play as Gordon hl2 episode 3, Shepard would be ok I guess, but it
wouldn't have the same "feel". That would also probably mean less interaction with Alyx to.
Edit: Gman pulled some strings in opposing force, to. In the room where the toxic waste is rising and there's no way out, you can see Gman opening the door for you. And when you get to where a group of other solders are escaping in a helicopter, Gman closes the door so you can't go with them then stares at you through the glass for a few seconds.