Freespace 1: Is a space-combat game, in which you take part of a series of missions against the enemy known as the Shivans. There is not much of a plot really, so for the most part, this can be skipped. The real fun is in how the game lays.
When I first tried Freespace, I was almost dismissive of it. You take on a series of missions, in which you attack an enemy formation. There are a few missions, where things are different. Escorts, and stealth/spy come into play, but basically your ship is a fighter.
As you progress, you gain access to new technology. Ships range from your basic attack vessel, to bombers and interceptors. Weapons become more and more powerful, and have different rates of effect against enemy hull and shields. Missiles are dumb-fire, lock and heat seek.
The combination of all of these allows you to select the way to complete each mission.
Graphically and Soundwise, it's fairly simple...
If it sounds like, i'm struggling to say something here, it's because it's true. Freespace, at it's core, is quite simple. But with some stunning actual gameplay that's hard to put into words.
Fighting is quite intense, and requires attention and reflexes. To aid you, you can command various fighter wings. The whole keymap is huge, and while you don't need to learn all 100 or so keys, it will help!
This is simply they type of game you have to try. There might not be much to it, but again, it's very well done.
If you do enjoy it, go out and get Freespace 2 immediately. The scale of battles is increased massivly, capital ships are huge and take some time to navigate, enemies are more clever and everything just feels highly polished.