This is a punishingly difficult campaign, even on Medium. I've finished it twice out of I-don't-know-how-many attempts.
That being said, I love all the little bits of lore and attention to detail, like how the Terran pilots speak in Simlish, the Vasudan fighters have their own Vasudan-specific weapons, and
how the lights flicker and go out on the Legion after the Lucifer bores a hole through her.
A few possible bugs:
I don't know if it's intentional, but the Guardian will not ask for reinforcements when the Radru cruisers jump in if its engines are disabled soon after; it will only call for help if someone is around to play bomber defense and keep it operational (and even then, the engines are scripted to blow out after the third wing of bombers is destroyed). This is how things will play out for most players, as they will probably be occupied with all of the other Shivan craft in the area, and it makes the "defend the Guardian" part of the mission much harder.
The Lucifer's shield animation is not showing up. Is this so it can take damage?
Does the Avenger use a special damage table in this campaign? Or has the enemy AI been tweaked for better shield management? Maybe it's because you're mostly attacking bombers, but it feels like it takes forever to get Shivan shields down, even on a Basilisk.
The first time I played this mission and used the checkpoint system (after the fighter screen was wiped out), the action in the mission stopped; I blew up the Cain cruisers, but nothing happened afterward. However, I've been unable to reproduce this behavior.