The intro video for the original "Left 4 Dead" was one of the best pre-rendered cutscenes I've ever seen. It so perfectly captured the spirit of the game (killing zombies), effective tactics against the special zombies, and the personalities of the four survivors. It was funny, intense and visually excellent.
Valve's high standards have apparently continued on through to "Left 4 Dead 2," as seen in the leaked intro video for that game: