The Seven Hour City
Kill Screen has a terrific article up about City 17, from Half Life 2, exploring what makes it such a wonderful introduction to the game's themes and mechanics:
Full Story: HEREI step off the run-down train onto the platform, and a bright, white light fills my vision. The beeping surveillance robot hovers away as my eyes adjust, and I begin to see glimpses of the world I’ve stepped into; the world after the war. They say it only took seven hours for the governments of Earth to surrender, and the evidence of that subjugation is all around me. A fleshy alien hunches over the broom it's chained to. Loved ones anxiously await friends and family who will never arrive. A large arrivals and departures board displays cities stripped of their identities and compartmentalised, much like their citizens. I am herded through security checkpoints and dimly lit hallways. Eventually, I make it outside, to a quiet city square carefully watched by the occupying Combine forces, and overshadowed by the phallus-to-end-all-phalluses: the Combine Citadel. This is it. This is life in the Seven Hour City. City 17.