well, i think everyone here already knows the ending to both, i never completed HL1, but HL2, basically, gordon gets to the top of the citadel and blasts the holy crap out of that evil doctor dude (i forgot his name) who is trying to escape to the alien realm (XEN, i believe), in shooting the crap out of him and his massive energy amtter transporter thing you kinda cause a breakdown of every atom possible and make everything go kaboom, just as your skin is about to be ripped from your bones guess who walk in from nowhere and stops time..... yup, that damn G-Man. He saves you and alex, but thats where it stops, left wide open for a sequal or 4.
yeh, i know a bit sketchy, but im just outlining for ya....
draogn