Let me start by saying that this is definitely one of my favorite user-made campaigns, and it was so good that I reinstalled it for yet another playthrough after I lost my hard drive.
Although, there were a few things I noticed on the subsequent playthroughs that rubbed me the wrong way. I figured I'd post them here for the sake of, as the topic states, constructive criticism.
First, some of the writing seemed a bit like ham, particularly the phrase "sweet fortune." I dunno, maybe it's just because of the lack of voice acting (for example, if you just read Shakespeare, it sucks, but when you see it performed, that's something else altogether.) And maybe you tried to come up with a brand new phrase, since a language is bound to change in a few hundred years. If that's the case, disregard this part. The writing itself was good, at any rate. It had an eloquence to it that seemed natural - the vocabulary was varied and rich without giving the feeling that the author was addicted to his thesaurus. "We'll make it [...] I swear" beats the hell out of "HANG ON, DUDES," at any rate.
Second, and this may just be personal preference, a couple of the music tracks just sounded... wrong. Particularly the track that played when the Ravana appears at the end of Forced Entry. It's just jarring to have a campaign full of epic orchestral and electronic music, only to be smacked in the ear with a fairly cheesy Playstation One era MIDI track. Again, that may be personal preference. I'm a big fan of consistency and auditory coherence, though, and I'm sure I'm not alone.
Thirdly and finally, some parts of the campaign seem to suffer from what I call Halo 2 syndrome, in that with some frequency you simply fail/die without there being much you can do to prevent it (those who've played through the Halo 2 campaign might be familiar with this). This often has something to do with a Lilith (Freakin' HATE those little bastards). In the Vishnan mission where you have to protect the arbiters from a Lilith, I found that it was virtually impossible to stop it in time unless you started flying towards it before it jumped in. While attempting to destroy the Sathanas, I had to retreat to a friendly corvette once it arrived since all the non-Alpha wingmen died and a wing of Dragons jumps in shortly thereafter (fighting six dragons in a Boanerges = not fun). Maybe I have the worst luck, but through no fault of my own I failed the last mission about nine times (ship defenses shoot a megabomb just as a fighter launches one right next to me, a Rakshasa smacks me while exiting subspace, crap like that.) It seemed like the first half of the campaign played flawlessly, but it also seemed like the latter half could have used a bit more playtesting. Of course, I have a tendency to get violated by Murphy's Law no matter what I do, so that might also have been the case.
Let me close by saying that I did truly enjoy this campaign. The presentation was a cut above, and it had a quality about it not present in much of the user-made content out there. By posting this, I'm hoping to maybe give you a few areas to improve on in the next chapter.