Alright, I will give my review.
Since this is a simply harder version of "Legacy of the Damned" campaign, I paid attention only to gameplay, rather than grammar or bugs, and I only checked the missions you mentioned.
Note: my version is 1.31.1
All chapters:
-If I decide to quit the mission at any point, even at the start, the campaign screen doesn't show any map to be selected. I have to go back and select the campaign again
Here is the demonstration
Campaign Screen | HIVE
Chapter One:
-If you want a lore-wise opinion, the Scourge was never capable of taking control of revenants
Chapter Three:
-While playing, I very rarely suffered any attack from Varimathras, and when I eventually attacked, I found it quite easy to destroy. So I restarted the mission and used the "iseedeadpeople" cheat to check Varimathras' forces and I saw demons attacking Varimathras' undead base and Varimathras himself. The demons are part of another team named "Varimathras' Forces", and yet they are considered neutral towards me (their team's name was yellow-colored). They trashed nearly half of Varimathras' base.
Chapter Six:
-Varimathras has Rain of Fire and Finger of Death (which share the same F hotkey) and Doom and Animate Dead (which share the D hotkey)
-Why Sylvanas has Piercing Damage rather than Hero Damage in this mission?
-Good idea to put another Dreadlords in Balnazzar's camp. I always found it odd that, while we faced dreadlords in the previous campaigns, there were only four dreadlords left by the time of "Legacy of the Damned"
-I am not sure if Varimathras, having betrayed the Legion, can enlist the help of Doomguards. Infernals and Felhounds, sure, but Doomguards?
Chapter Eight:
-It is nigh unfair that Illidan can do all that damage, while Arthas is around the same stats he usually has. But since this is a Brutal campaign, I will let that pass...