Gotta (partly) agree with Decker. The Earthsiege/Starsiege Universe is an amazingly cool one. Not sure how much is fan made but there's a cool archive on the Starsiege 2885 (?) site with the timeline. The orbital defense of earth would make a class Freespace campaign.
I was addicted to Earthsiege 2 back in the day. One of my first PC games. I was really disappointed with Starsiege though, which I also 'acquired' some time later. It just completely changed the gameplay dynamics. The HERCs to me felt really underpowered and unarmoured. But in fairness I guess they were trying hard to move away from the Mechwarrior type of combat and differentiate themselves. And while the plot and briefings were really cool and built up an amazing atmosphere I just didn't think it was relayed well in the mission.
of that would be technical limitations of the time but still, they were all pretty similar and usually very easy.
The Cybrid campaign was especially bad. Had to do, but I think it failed miserably to convincingly convey the overwhelming superiority of the Cybrids (at that moment in time with Terran forces divided) and come up with a reason for the challenging missions.