This time you are sent in to Black Mesa for an entirely different reason – Giant Scientists!
Big Scientists have their visual appearance scaled up, but not their hitboxes. This means that to kill them, you have to shoot between their feet (especially once they get above 30ft)
Marines are your friends, the only exception is in the test chamber level (this is due to a bug I cant fix). The ones that attack you are the ones which come from the roof of the chamber, they usually arent a problem as they get killed in the crossfire.
During the intro in the chopper, watch the window (this is where all the magic happens!)