So, I played this through a little while back. Mostly for the simple reason that I just wanted to fight the Nightmares, to be perfectly honest.
It was good -- far better than I was really expecting based on the first couple missions. (It took me a week or two to return to it after playing those -- first, I had to figure out how to switch the zoom key because I use D for yaw right, and then I ran into a bug on the second mission where landing on the carrier wouldn't end it, and it was a long mission so I didn't want to restart right away. When I finally did, it worked fine.)
And the writing was honestly quite good. On a small scale, anyway. Large-scale, the plot is almost identical to FS2, except that destroying the Sath-equivalent actually works.
(Until the secret missions, anyway, which I haven't really played.)
Two questions. One: why'd you name it the Hiven? It's...not a very compelling or scary name, and I always just ended up thinking of an NPC from Star Trek Online (although that part is hardly your fault). I was expecting it to be the name of some demon or something, but Google didn't turn up anything. Is it just derived from "hive"?
Question two: what's the track labeled "ToYptWE", or something along those lines? It's used as the main battle music in the mission where the Nightmares first appear. It sounds Mass-Effect-y, but I wasn't able to find it in the ME2 OST.