Freespace is only outdone by its sequel Freespace 2. If you want some incredible space sim action with an incredible storyline and some pretty amazing graphics that hold well even today. You can't go wrong with Freespace.
The missions are varied, there are plenty of ships and weapons to work with and the sense of scale is impressive. If you thought games like X2 or Tachyon had scale, you can thank Freespace for pioneering it.
You'd be missing out on one of the best of all time if you didn't pick this one up.