After too many failed attempts to buy Half-Life 2 Silver via that Steam thing, I decided to just buy the regular DVD version in the store last thursday. Which installed fine, yay!
I'm playing it on Hard to make sure I don't breeze through it too quickly, which seems to be working: I'm already going to have to go back to an earlier saved game because I won't be getting past those manhacks with no ammo + 15% health. An opportunity to enjoy the amazing scenery some more.
This isn't going to work...