There is a community of dedicated fans at Hard Light Productions that have created a wonderful thing called Freespace Open, which improves gameplay, graphics, and brings a whole range of new campaigns to the field. You need a full version of Freespace 2 installed. GoG's version works perfectly. It also gives you "Freespace Port" which allows you to play Freesapce 1's missions, with full voice acting and music. With the bonus graphics!
The community has also re-made Silent Threat, cleverly named Silent Threat: Reborn. All worthy of the highest praise.
www.hard-light.net