Somewhere in the middle of Half Life 2, the player assaults a small Combine base. The base itself is fairly nondescript, merely another place for Gordon Freeman to massacre some bad guys. All the while, the player notices a huge bridge in the background.
The player ducks into a building, heals up and arms himself for whatever is coming ahead, then heads outside to find...
If the above screenshot isn't too impressive (and it's not) trust me, the real thing is startling. When I first played it, it froze me for a moment. Falling off this bridge turned out to be one of the most blood-freezing deaths I've ever experienced in video gaming. I think a lot of that is due to the "sack of potatoes" falling physics. There's no 'float' here, just a sudden drop to your doom.
An underrated and perfectly done piece of the game that comes seemingly out of nowhere.