Tachyon is an excellent game to me, but a little to linear. As stated, you start out working for a corporation and due to some really bad luck you get banished to "The Fringe" of space. Once there you start your life over again trying to create a new life.
The story line leads you to a point where you have to choose one of 2 paths, either the Mega-Corporation side (Galspan) or the Boras. Once you choose a side, you can't switch without restarting a new game. While both offer a variety of missions, the overall plot remains the same. Do what they want, and in return they'll help clear your name.
First time through I played the Galspan side, and I felt like a criminal at times due to the nature of some of the missions. I'm not saying this is a bad thing, just unexpected. There are a few side missions that have no bearing on the storyline except they give you a chance to pick up a few extra credits for ship upgrades. Some of these side missions are tedious, and others got on my nerves.
The AI is decent, but some of the AI ships seemed to hard to destroy. The pilots didn't do anything spectacular, it's just that their ships took an inordinate amount of damage before dying. The graphics were excellent IMO, but not the best I've seen in a space game.
Being a fan of Wing Commander, Privateer I was hoping for a more open ended game in terms of mission selecting and the story line. However this game is pretty much as linear as they come. Finish mission A to be allowed to go here. Finish Mission B to go here, and so on and so on. Do 3 or 4 missions per space station, and soon you'll be heading home with your name cleared. The only freedom is that you can choose which order to perform the 3 or 4 missions at any given space station.
Overall it's a good game with excellent graphics but has a few problems and is too linear for a space game. Still it's worth the price, especially since it's a bargain bin game now.