Generally regarded as a friend rather than a foe because he is your employer in the game. In HL1, he was considered an enemy, however, so this is all just speculation.
From what I can tell, primary ally in the game. As the daughter of a scientist in the first game, she'll probably play some integral part in the story line
Hero of the first expansion pack for HL1, making a cameo in HL2, and this time, helping out the main hero.
Apparently you'll be able to control these throughout the game, at different times.
Go figure...
Once again, no one save valve knows virtually anything about this, at all. I couldn't even tell you if this was a human, or some kind of alien.
Darn, eh?
I can safely say that this enemy is an alien.
I can also tell you that it may be quite tall.
Probably prowls quite a bit, and probably doesnt like you.
This is so mysterious that I can't even find an actually game image of it.
THIS one I can tell you about, considering that it's the exact same as the one in the original half-life.
Zombies are created when annoying little aliens inventively called "Headcrabs" attach themselves to the faces of your comrades and buddies, taking control of them and turnign them against you.
Slow, fairly easy to kill.