In the meantime, I'm waiting for Half-LifeĀ² : Episode 3.
I first played the game solo... It is so creepy, so frightening that it can't be described unless you try it yourself. Cheap screamers but also a very polished atmosphere both await the player at every corner of the streets.
Then I played coop... And it is way way less scary when you have the moral support of your teammates. Still, it is a lot of fun when finishing off giant creepy monsters with nothing but a tree branch because of the scarce ammo.
Play it. If you're too chicken, play coop, but just play it.