You know, the original Source engine is still going pretty strong with all the mods that people have made for it - They Hunger, Sven Co-op and Afraid of Monsters being only a few.
I found this video years ago on YouTube and rediscovered it recently. I never would've thought that two nutters messing around in a server with the admin from hell could amuse me so much. Their exploits culminated in a final live stream (which was also recorded from the PoV of the tormenting admin).
The admin plays the part of the titular protagonist of the mod - David Leatherhood - and the other players in the server must suffer through a series of maps in which he has the power to make them endure the kind of hell they never thought possible. The man has it down to an art form.
I think the misadventures of these two long-suffering friends adequately demonstrates the endurance of the engine, its mod tools and its tenacious player base, as well as every admin's struggle with the Inner Bastard. Favourite mod and pretty good engine, hands-down.
EDIT: Also, the comment button doesn't seem to appear at the top of these articles like it usually would - in this case, it's only at the bottom, while in other articles it appears at both the top and bottom.