Half-⁠Life

Valve took a reworked Quake engine and put its effort into continuity. The action starts with a tram ride during which there is nothing to do but look around, and from then on the camera is never taken away from the player: there are no cutscenes or title cards between levels. The story plays out right in the space of the level: a script fires when the player reaches the right spot, and the characters talk and act nearby while the player is free to leave or stay. Hence the silence of the main character: he doesn't take part in the conversation, he is present at it.

The soldiers who arrive in the second half work as a squad: they cover each other, flank and retreat, so a firefight stops being a matter of clearing a room of monsters. Soon after release, tools for building levels and mods appeared, and outside projects grew on that base, among them Counter-Strike.