Like Star Control II? This game might be for you! Epic space-exploration, Wing Commander-esque combat-- save the galaxy!
At first, the only plot you get is that a spaceship crashes on Earth, and the government repairs it, and sends you out into space to find out where it came from. As soon as you enter orbit around Earth you are hailed by an alien ship, and its occupant offers you membership in the Alliance. Whether or not you choose to join will vastly affect the rest of the game.
You can explore dozens of star systems and planets, trade, chat or fight with numerous different races, each with their own theme music and voice samples. Later in the game you can trade for bots that can be sent down to planet surfaces to harvest gas, minerals, or various foodstuffs. These can in turn be traded for better weapons and equipment to help better withstand enemy attacks.
The more people you meet, the more you will learn about the enemies you face, known as the Korok, where they come from, and ultimately- decide the fate of the galaxy.
The game could be buggy at times, with the sound not always loading up with the rest of the game, and it's not easy at first to figure out what to do, but if you can find this game on the internet or in a bargain bin somewhere, it's worth a play through.