I will admit, though, some of Timothy Zahn's novels haven't blown me away the same way the Thrawn Trilogy has. Choices of One was fun and I liked the Outbound Flight Project plus its companion novel in Survivor's Quest but they were just good rather than great. I loved the Hand of Thrawn duology but that had the benefit of being the grand finale to the "Bantam" Star Wars Expanded Universe. So, where does Thrawn stand? Especially since it is the first "canon" novel to star Grand Admiral Thrawn? Around the Hand of Thrawn duology and better than most but not up there with the Thrawn Trilogy.
The premise is basically, "The Adventures of Lieutenant Thrawn, Officer of the Empire." It's kind of a weird Horatio Hornblower collection of adventures which chronicle his ascension from naive every Chiss to the 4th or 5th most powerful man in the galaxy. It also expands on, more or less gives, a backstory to Governor Pryce from Star Wars: Rebels. The book doesn't deal with any great threats to the Empire. There's no superweapons, alien races, or possible origins to Snoke and the book feels a bit subdued to what I think of as typical Star Wars fair.
I was a bit annoyed with the opening few chapters because they're more or less a retelling of a short story ("Mist Encounter", SWAJ 7#) which Timothy Zahn wrote for Star Wars: Adventure Journal back in the day. Given it was published in 1995 in a periodical no longer commonly available and was a pretty good story, I don't hold this against Timothy but it was re-rereading events I'd already read. The subtle changes also threw me, like the introduction of a new character not in the original story but playing a vital role in Thrawn's life.
The book proceeds to follow Thrawn as he goes to the Imperial Academy with Eli Vanto on the Emperor's orders, deals with several pirate groups, and then becomes involved in a massacre mentioned in Star Wars: Rebels that gets him promoted to Grand Admiral. I enjoyed these sections a great deal but they confused the heck out of me because I find it difficult to believe the Emperor would just put Thrawn in the general Imperial Navy. I would have assumed he'd have given him a Captainship or Admiralship to begin with as he's such a valuable resource on the Unknown Regions. Also, I don't believe the Emperor wouldn't get every bit of information on them from Thrawn, including the location of the Chiss. He's not a very accommodating man.
The book also continues Zahn's portrayal of Thrawn as "The Good Imperial." This Thrawn is, with one exception where he returns Wookiee slaves to their captors, a thoroughly decent man who just so happens to be working for a tyranny. There's also a potential retcon to his motivations that he may not even be loyal to the Empire at all but just using it for his own purposes. I can't say I approve of this as while I like "decent people in awful service", I have to say I prefer Thrawn having a bit more edge and ruthlessness. Indeed, the book retcons his role in the Rebels massacre to being the fault of another.
I was actually more interested in the story of Arihnda Pryce, the Colonel Spalko-esque villain of the Rebels cartoon. It's an interesting take to have her be a small town girl in the Big City who ends up becoming a ruthless Space Nazi but Zahn doesn't pull any punches in her corruption. Indeed, I felt she was a bit too fast in her corruption. Hypocritical as it may be, I wish she'd been a little more redeemable by the end. Really, Arihnda's story shows why so many Imperials would want to join the Empire. It serves as an alternative to the massive petty local corruption and can reward lavishly those who side with it over their home worlds.
In conclusion, this was a decent book all round and had a lot of Easter Eggs for the fans of the Rebels cartoon. I felt Thrawn was a bit too nice in the story and would have preferred to see him more willing to spill blood but enjoyed Pryce's humanization. It's probably my favorite canon book release after Lost Stars, Bloodline, and the Aftermath Trilogy.