Half-Life changed shooters by refusing to interrupt them. There are no cutscenes. The story happens around you while you keep control, starting with a tram ride through Black Mesa that tells you everything about the place before you have fired a shot.

Gordon Freeman never speaks, and that silence is deliberate - he's a vessel rather than a character, which is why the people around him do so much talking. Valve's writing works by having scientists and soldiers react to you rather than at you.

The crowbar is one of the most famous objects in video games and it is, functionally, a starter weapon you outgrow in ten minutes. Its reputation comes entirely from what it represents: a physicist solving problems with the nearest available tool.

The headcrab remains an excellent piece of monster design - small, fast, and responsible for the one enemy type that makes players genuinely tense in corridors.

This collection covers Black Mesa's equipment and residents. Still waiting on the third one, obviously.