Although the game will eventually force you to choose one of two main branches, the corporate mercenary or the freedom fighter, it offers a lot of choice in terms of which missions you choose and what kind of ship you fly. This choice is a bit of sleight of hand, but it works. The missions are all canned and arranged in an obvious branching structure, but this is much better than the standard "A then B then C" arrangement of most mission based games. There are five basic ship types for both of Tachyon's sides, but they're almost strictly linear: the cheaper ships are useless once you can afford the expensive ships. Granted, some of the lighter ships are faster and speed is extremely important in some missions. But because of the way the afterburner works and the options for energy allocation, even the supposedly slow ships can get around in short order.
Tachyon has a great variety of weapons and components. For instance, you can buy sappers, devices that you can attach to enemy ships to slow them down, drain their energy, or remotely detonate. While this sounds fun in theory, in practice these devices are all but useless; for all the trouble you have to go through to attach them, the payoff isn't great enough. You might as well just shoot enemy ship with lasers. And there are no situations where you have to use sappers because other weapons aren't available. Similarly, a lot of the weapons and components aren't very useful. And you'll rarely find the computer-controlled ships using the more exotic weapons. After playing through both campaigns, there were perhaps a dozen occasions in which the AI used guided missiles or more exotic weapons like the railgun. Tachyon may offer a lot of variety, but much of it is squandered.