Well… I loved it. It may the only post-Disney reboot novel I'd emphatically rate full marks. This is Thrawn's genius fully exercised but not without credible challenge, and Zahn depicts him both at his best and coping with failure and obstruction. Zahn also contributes more world-building exploiting his position as an EU author to fill in the finer details of the lore much like he pushed for when writing the Thrawn Trilogy.
My complaints about Imperial speciesism are actually addressed by the characters in the novel with plausible explanations. The dialogue hashes out why even species loyal to the Republic didn't always get reprieve and how much dissent exists on the matter between corward and rimward worlds. The moral rot in the Empire is portrayed as a contrast between the source of the cancer that ate away at the Republic and the efforts of idealists trying to bring law to lawlessness.
I know many people were disappointed by Thrawn's debut in Rebels thinking that the cartoon's writers cheapened him by explaining his rise to Grand Admiral be the result of destroying a sector's insurgents at a high cost of civilian casualty's. Zahn handily retcons that in this novel by portraying it as the treachery of another character on that show whose selfishness undermines Thrawn's best efforts, which serves as a micocosm of the greater friction between power for the ego and power for a higher cause that is a running theme in the story both among Imperials and Rebels.
For a lore hound like me, the best part is that there's so much elucidation. Every chapter begins with some monologue by Thrawn about his philosophy as a soldier and a warrior. Climax points in each act reveal something new about character motives, Imperial politics, and what goes on off-screen during the movies and cartoons. There's even a bit of backstory thrown in for Sheev and Vader.
This may be the only nuanced view of the Galactic Empire that "Empire Did Nothing Wrong" fanboys like me are going to get under (((Disney))), so I'd recommend at least downloading it. I bought the audiobook, personally, since I travel 30 minutes round trip daily and they help pass the time.