I second that. Definitively the best shareware game around, and clearly worth buying it (so you can go further in storylines, buy better ships and all).
To know how to start a particular storyline, check
this.
I know the game can look old at the first glance, but trust me when I say it's very deep and can require some skills at some point. Aah, the "Not The 9 O'clock" manoeuver...
There are some good total conversions around too, like Polycon and Starfleet Adventures.