Science Fiction: Subgenres (Part One)

Science fiction is a widespread genre. Everything from aliens to near future to intergalactic human empires, it encompasses just about anything you can imagine that can be explained, in some manner, by science. Magic becomes psionics, fantasy monsters become genetic creations. For this post I'm going to talk about three subgenres of science fiction to give an idea what they are about. Other posts will add to these.

Military Science Fiction
Space + Military + the Future. That's basically it. The great thing about this genre is that you have a huge range of options for dealing with military battles. Interstellar wars are common, wars between humans and aliens, or even humans and humans are just as common. The most important thing about this subgenre is that the military is involved.
Imagine entire campaigns of war and you have an idea what this genre is about. It does, however, extend beyond that. If you look at Battlestar Galactica you'll see that there isn't a whole lot of actual war, at least in the first season, of which I'm familiar with. While there are battles, a lot of the episodes deal with espionage, conspiracy, and other things within the framework of a militaristic society. The military exists to protect the fledgling human civilization and has to deal with problems beyond war.
Examples: Starship Troopers by Robert A. Heinlein, Old Man's War by John Scalzi, Warhammer 40K, and Battlestar Galactica.

First Contact
Any time you read a story or see a movie in which humans meet aliens for the first time, that is a first contact story. That's the basic premise. Humans meeting aliens for the first time. Star Trek does this quite a lot, where Captain Kirk or Captain Picard find new species. That's sort of in the reverse, but you get the basic premise.
Examples: Star Trek, Mission To Mars, and Contact by Carl Sagan.

Dystopia
The infamous dystopia. Okay, it's not infamous, but it is famous. Dystopian novels are probably the most chilling of the science fiction breed because they intentionally draw upon all the darkest things you can possibly imagine about the human condition. Fallen societies, worlds crushed into the stone age, people preying on people for survival, governments ruling their people with violent force, etc.
There are enough movies and books out there to fill this genre to the tipping point. Why? Because it is a most loved genre. All that we hate about ourselves comes out in dystopian novels.
Examples: 1984 by George Orwell, Brave New World by Aldous Huxley, Parable of the Sower by Octavia Butler, V For Vendetta, and A Clockwork Orange by Anthony Burgess.