Considering it's a medium pretty much built on the art of murder, it's kind of surprising how few effective deaths there are in video game stories.
Sure there are still memorable ones - enough to do plenty of lists on them in the past - but considering how much death is dealt out in the average release, only a small percentage of them leave much of an impression on the player.
After wasting so many nameless bad guys, it makes sense for fans to get a little numbed to virtual death, but one easy way to grab their attention is to whack a main character completely out the blue, with little warning and even less fanfare afterwards.
Sure, occasionally this is done purely for shock factor, but there's no denying that a swift drive-by of a death works wonders in slapping the player in the face and making them pay attention. Hell, Game of Thrones pretty much made its living off this brand of brutality.