Originally Posted by epmode
aight. spoiler tagged for anyone that didn't beat the first game:
you eventally make your way to xen, the alien homeworld, where you fight some hideous boss thing called nihilanth. it's implied (can't remember if it was specifically stated,) that following the resonance cascade, nihilanth has been teleporting hundreds of monsters to earth. after launching a few rockets into its brain, it dies, effectively ending the invasion.
you then find yourself weaponless, in front of the g-man. seems that you were doing his bidding the whole time, as his troops are in the process of conquering xen; a much easier task without its overlord. anyway, the g-man gives you a choice: work for him, or die. after accepting his offer, the screen goes black and the following text appears:
SUBJECT: FREEMAN
STATUS: HIRED
AWAITING ASSIGNMENT
roll credits.