Written while mostly dead of tiredness. Read at your own risk.
Nostalgia is the most powerful and underused technique in game writing.
Nostalgia is an exceptionally powerful emotion in general. You distill your experiences and simmer them down into a blend far more potent than the original experience. Add a dash of "how things have changed" or "how things haven't changed", and it's flavored to taste.
Lots of the most powerful stories use nostalgia, especially serial dramas such as Smallville and any fairly long book. Almost all the stories people tell about themselves are seen through a nostalgic lense, condensed and purified. Nostalgia makes people think they were having a great time playing that MMORPG or that they would have been happier with their high school sweetheart.
Nostalgia is most potent when the audience has time to let it simmer. It's really potent in serial dramas because they are spread out over months. However, a dash of nostalgia could be added to nearly every game, given that few of them are less than ten hours long.
The thing is, nostalgia is a complex thing. You can get nostalgia from a number of sources, but they all spring from one basic fountain: memories of a different view point.
For example, you feel nostalgia when a series ends. The viewpoint has changed, and you feel a bittersweet yearning for the adventure of the series. You wish it would continue, that adventurous (or melodramatic, or whatever) view point.
You feel nostalgic halfway through the series when something changes. Maybe someone dies, or two people break up. With just a touch of the artist's brush, you feel nostalgia for the viewpoint that had been developing - perhaps even a viewpoint that had never actually come into being, but you expected. Like the failed love affair - ah, what could have been. That viewpoint that never happened, but could have.
That idealized virtual view point is what nostalgia is about. A few games have used this. Aerith dies, and you feel a painful spike. That spike is caused by the severing of a view point. It is a type of nostalgia, although a brutally sharp one that deserves to be called by a different name: loss.
But you can't really say that loss is the emotion you're going for. What you're going for is a lost viewpoint, a severed future, a reality which no longer exists for you. It is a kind of loss, but the emotions you get vary depending on the kind of loss and how the writer frames it. You could even feel joy thanks to your loss: the loss of a potential future where you're tortured, for example.
The key is that the audience has to have two attributes: they have to know what they lost, and they have to have put emotional attachment into it. The first is relatively easy, and can be done with simple cues such as playing that certain song, or seeing that certain person riding into the sunset, or having a flashback.
The second - emotional attachment - is more difficult. How do you get the audience emotionally attached to your viewpoint? Mostly, it's a matter of time. Emotional attachment's biggest factor is time spent exposed to the matter. The time spent mulling over the matter also counts, and people will spend more time mulling it over (if given time to mull it over) depending on its emotional content. Think of it like this:
Attachment = emotion squared + length
Where emotion is 1-10, and inherent in the squaring is the mulling time.
Obviously, this is rather guessy.
Now, a serial drama might have 5 emotion and 25 hours per season. So, we get 5 * 5 + 25, or 50.
A good movie like Aliens might have 9 emotion and only 2 hours. So, we get 9 * 9 + 2, or 83.
A solid game might have 4 emotion and 50 hours. So, we get 4 * 4 + 50, or 64. Of course, this will vary depending on a few factors: how much time the player spends mulling the game over while not playing, whether he is impressed by the gameplay (effectively raising the emotion rating), etc.
By my ridiculous oversimplification, it is fairly clear that games can compete with great movies and mediocre serial dramas pretty easily when it comes to emotional investment.
This means that loss and nostalgia in a video game would be just as powerful.
So use 'em!