Half-Life 2: Episode One mod
Up until now, I wasn't aware of Adam Foster's highly-regarded Half Life 2 mod MINERVA in any real sense. The name sounds familiar, so I'm sure I had at one point or another come across it within the last few years, but I never bothered to go through with installation for whatever reason. Now that the game is on Steam -- and people still seem thrilled by the mod -- the excuses are dwindling. You'll just need a copy of Half-Life 2: Episode One to play.
MINERVA was notably the project "which got me a job at Valve," says Foster. This specific build has been updated with "tweaked visuals, bug fixes, better puzzles and all kinds of subtle improvements. Nothing hugely new, just old stuff tidied and polished for this re-release."
Looks like I have some weekend playing ahead of me.