This book was an enjoyable read for me. True, not terribly much actually happens (since the plot is only setting up, presumably, the conflict of the movie), but as a piece of pure character-exploration, it made me fall in love with Tempest Shadow. I'm eagerly awaiting the movie so that I can see her in action, and hopefully come to a satisfying resolution of her arc.
If you're a parent looking to screen this book before giving it to your child, rest assured, you've not got anything to worry about.
If you're an older fan looking to indulge in more of a backstory for the movie antagonist, Tempest Shadow, this book certainly does provide more of a fleshed-out backstory and character history for her than the brief flashback we get in the film in her song sequence. Bear in mind this is written for readers as young as 6 y.o., so if you're hoping for any eloquent, emotionally-gripping prose, you're probably better off seeking out fanfiction. Mostly just because, well...the book is written for kids, so the actual writing is pretty simple. I personally don't think this is a bad thing; heck, if you're just looking for a quick read, you could finish this in under an hour. I would also strongly recommend seeing the movie first and then reading this. Trust me on that one.
I think my only qualm with this book, both as an MLP plug-in and a movie tie-in character story, is the timeline. Reading through the book, it feels like there are multiple conflicts or at least head-scratching points where the timeline is supposed to intertwine. I won't give spoilers, but suffice it to say that the book mentions events from the series and the film that don't seem to add up in the timeline, and it's also difficult to determine the timespan of the book itself. We start with Tempest's earlier years, and by the time the book ends, it's only a week before the Friendship Festival that opens the movie. And as Tempest is canonically stated to be the same age as Princess Twilight Sparkle, we have to assume that a lot of time has passed from the opening of the book to its close. It certainly doesn't feel that way when you read it though. Again, that could just be due to the fact it was written for a child audience, as the assumption is probably that younger readers wouldn't track the span of time all that closely.
Keeping in mind that this is a children's book, the complexity level was very low. Unfortunately, I don't just mean in the sense of syntax and diction which would be naturally expected at the intended reading level; I am referring to emotional complexity. I felt a certain level of disconnect with the main character and don't really understand how she goes from hesitant to cause harm even when stealing to willing to throw her home country under the bus and subject it to an invasion. It comes across as a bit of a quick-switch and feels as though there should have been more build up in between. It's possible that I as the reader am not connecting with the character's anxiety and desperation properly. Her transition to a constant liar / connoisseur of half-truths over the course of the book is fortunately much smoother and doesn't come across as rushed.
In short, the backstory is solid and does provide a viable 'why' for how Tempest Shadow becomes the ruthless commander the movie trailers have painted her as, but some of the emotional transitions do not seem to flow smoothly in the narration.
About 100 pages of table-setting for what is probably a better story. A young unicorn is rendered disabled (by Equestrial magic standards) and while struggling with a mixture of emotions, ends up on a winding road that leads to a dangerous precipice she's about to jump off of right into the thick of the tale that makes up the movie coming out in a few months...and then it ends. "To be continued". A 5-year old reviewer was begging for more, but also grew somewhat bored in the middle, softly demanding the Mane 6 arrive to spice things up, and wondering aloud when Baby Flurry Heart might make a cameo. This reviewer could not answer such questions, only knowing the Baby Flurry Heart lives in the Crystal Empire, which was not mentioned in this book. Spoiler alert: There is a partial Mane 6 sighting right at the end of the last chapter. I feel slightly less a man having written this.
I mostly liked this for a few good moments and for the characters. Sadly, this book feels like it was done quickly. I also felt like the writing was done too safely even though it's meant to be a book for younger readers. I dislike books that dumb down and put safety gloves on the plots and characters just for the sake of not upsetting anyone, and I felt this book tried to do that to some degree.
Also, I feel like the timeline of events in the book doesn't really match up well with itself or with what we know from other sources. In general, it felt like it needed a little more work on both the part of the writer and editors because it could have easily been improved.
I wanted so badly to like this book more. I felt like the writing was rushed in an effort to get the book out in time for the movie. That being said, it was still a good, quick read and I liked it, didn't love it, but I liked it. It was nice to have Tempest Shadow's backstory before seeing the movie.
If you didn't (or weren't forced to by your kids) watch the movie, do that first as this book is a prequel and only really makes much sense with the movie's story to fill in the gaps. A fun little read with more character development than you might expect in a children's cartoon novel.