They made Gordon simply a tool. He's nothing more.
He's an MIT graduate. A theoretical physicist. I don't care how much they play on him being a "tool" or what have you, he's so far from fitting the profile of handling combat as he does that even when the first HL came out and it was still common they were trying intentionally perpetuate that kind of stereotype of implausibility in FPS and PC games in general.
Then they went through and had the kick-ass expansion,
Opposing Forces, made for the first game; detailing CPL Shepherd and the soldiers' side of the fight. I mean, the first dump truck-sized hole in the story line (in Gordon) would be plausible on its own, but CPL Shepherd, whom is still the only character they haven't brought back yet, makes me think they'll tie up a few loose ends by the time the series comes to a close.
Oh, don't get me wrong, I like Gordon. Even if he's a mute, if someone's going to bring back the panache of combat that only the DooM marine could seemingly have (that rucksack of his WAS really huge), it'd be him.
As for Alyx
Alyx... I liked her character in Ep1, just not how she was presented in the story. That probably doesn't make sense, but you know, you really just retreaded old territory in the game, going back into the Citadel and all, then playing bodyguard later on (was not cool with me at all).
Maybe this "exodus" they've got planned from City 17 as part of the storyline will get it back on track. I don't mind instilling some humanity into my game (I liked that about HL2, the rebels felt "real" and somewhat genuine in their fight), but I don't care for masochistic girlfriends.