Another Freespace - cant imagine all the possibilities. I tried to play X3 Reunion but you can't compare those titles. Freespace and Freespace 2 are legendary.
Add planet jumps, atmospheric flights, more simulation-like physics, free world, ship mallfunctions that can [for example] disable your reactor for a while and you drift in dead space , "side quests", capital ship controll anc crew manager, add some strategy elements like space shipyards more pilot-pilot interaction, some kind of "tactics development tool" where you can determine how your or other wings react when certain things happen (example - auto "cover me" if there are 2 or more ships on my tail], for higher rank officers possibility to create own missions within the storyline, by determining the goals and preparing a short briefing, add wing management, where you choose [with proper rank] pilots in your squad, and every pilot has a different role to play in the story. Bring back the Ancients, bring all the goodies
Hooked ;P