Inferno was really mostly a patchwork of fs1 and fs2, with a couple of filler ins for what would be thought to be fs3. Fs1, the shivans come out of nowhere suddenly. Fs2, having a civil war, and fighting the shivans. Fs3, a knossos to earth was built, and gtva has more efficient beams.
I can see why perhaps they wanted to redo the story. It was fun gameplay, but the whole grim story line thing wasn't there at all. It was like the damn shivans aren't able to kick ass anymore. Inferno was so non-fs, it really turned me away from it, derelict was a lot better. But, inferno alliance looks great and i need to give it a try, and i'm waiting eagerly for the revamped inferno r2 (besides the new ships, i hope the story is better).