The premise of the books is a variation on Romeo and Juliet in Space. In this case, aristocrat Thane Kyrell and rural poor-girl Ciena Ree are born on the same planet in the Outer Rim territories. Both of them are extremely good pilots, though, and manage to qualify to go to the Imperial Academy on Coruscant due to a chance encounter with Grand Moff Tarkin on a good day. Once enrolled, Thane Kyrell becomes increasingly disillusioned with the Empire while Ciena becomes increasingly fervernt. The pair fall in love but their politics manage to separate them just before the Death Star's completion signals the beginning of a new age in the galaxy.
The story rests on its protagonists with Ciena Ree being a Force-believing, moral, and exceptionally idealistic young woman. I.e. She's the person you normally would think would be drawn to the Rebellion. However, Ciena Ree comes from a culture which strongly emphasizes oaths and tradition. Once she's sworn allegiance to the Galactic Empire, that is it and you don't go against your home government. Thane is a snooty rich kid but he has a passionate loathing of authority thanks to his abusive father and sees that attitude everywhere in the Empire.
Honestly, Thane is a character which didn't need to be one of the protagonists because he comes off as a fairly vanilla character compared to Ciena. We've seen kids with daddy issues and disrespect for authority join the Rebellion many times before. He could have easily been a supporting character in Ciena's story and it would have probably made a (slightly) stronger novel.
Ciena Ree, by contrast, is a fascinating character who has a lot of dynamic changes over the course of the story as well as several interesting moral dilemmas. She wants desperately to believe the Empire is the "good guys" and even manages to rationalize away the destruction of Alderaan before the creation of a Second Death Star destroys even that fragile collection of delusions. Her status at the end of the book is questionable and I'm honestly interested in a sequel because I'd like to know what happens to her.
I like how the characters Forrest Gump their way through various events in Star Wars without feeling too forced. After all, they're assigned to Darth Vader's flagship and the elite of the Rebellion, so they're always going to be just off-camera so to speak. It gives a nice "boots on the ground" perspective to the cosmic conflict between good and evil going on around our protagonists.
I also appreciated the handling of Ciena Ree as she's a good deconstruction of the "Good Imperial." A lot of Timothy Zahn's writings show Imperials as just normal people following their government and questioning why it's so bad to be a soldier for the Emperor. Ciena Ree's perspective is a nightmare for a moral person and shows exactly why you can't be a good person for an organization underneath Palpatine and Vader. Justifying their atrocities makes you evil or deluded.
Indeed, the one character who fell flat for me was Nash Windrider who is an Alderaanian Imperial who goes insane trying to justify his loyalty to the Empire after his planet's destruction. Ciena is repulsed by him and hates him for going after Thane Kyrios. However, Nash is doing the exact same thing she is doing and Thane tried to kill him so Ciena just comes off as a huge hypocrite.
Despite dealing with serious subject matter, the book is often quite humorous. One of the best parts of the book is how both characters completely misunderstand their respective factions. While Ciena Ree believes the Empire to be good and the Rebellion evil, Thane refuses to believe the Rebels could be as idealistic or noble as they claim. It takes Mon Mothma helping him through a drunken pity party to help him realize they are as down to Earth (Tatooine?) as heroes should be.
In conclusion, there's a lot to recommend this book and it is one of the better Star Wars Expanded Universe novels. This takes place in the post-Disney "canon" timeline but can be read by anyone who has watched the movies with no difficulty.