Scenes are just scripted events that happen in Half-Life.
This cool scene where an Ichthysaur catches a scientist
A neat scene where some Human Grunts holds up a scientist
Another scene like the above, but why don't the Human Grunts attack the Barney?
A neat scene where 3 airplanes fly above
This still happens in the current game, but it happens on the elevator's ladder
Another scene where a Human Grunt holds up a scientist