Magic horses, guys.
I really love the Valdemar books. They are a little bit fluffy and wish fullfillment-y, but they are a lot of fun and oddly progressive in a lot of ways. Valdemar is kind of the perfect fantasy kingdom in a lot of ways, with a monarchy, but a monarchy run by people who are guaranteed to be good people, at least, even if it doesn't always promise that they will be good rulers.
Talia is an easy heroine to like. She starts in an awful family situation that does not suit her at all and has no clue what is going on when she appears to be kidnapped by a horse. Her confusion is a great intro to the series as a whole, actually, because we readers learn what is going on as she does and it makes it easier to follow everything with a new universe. She also loves to read, which I love to see in a book heroine and don't feel I see enough.
There is some political wrangling going on, but as this is the first book in a trilogy the full explanation of what is actually happening is not solved. It does end in a solid place, though, and doesn't feel like a cliffhanger. There are mysteries still to be solved, but things end in a logical place for Talia herself.
Watching Talia learn how to make friends and come out of her shell and actually trust people is a large chunk of the book. It is a coming-of-age novel, for sure, although clearly set in a fantasy universe. She ends up in some danger and has to learn who to trust, but things end pretty well for her. Valdemar is not Westeros, and although some bad stuff happens, it is always offset by good.
The side characters don't do a whole lot of coming into their own in this novel, though they get further development later. Jadus and Skif probably get the most "screen time," though that is due to the fact that they end up being the most directly connected to the plots against Talia. They're good friends for her to have, and very different, though most of what I know about them actually comes out in other books.
The writing feels a bit rough in this one sometimes; there is a lot more telling than showing than there needs to be, though this is not as much of a problem in the rest of the trilogy. I think it was difficult to condense this much time and this many plotlines and this much new worldbuilding into a book of this size, and it suffers from that a bit. Admittedly, I have also always loved the Collegium and wished that more time got spent there watching the training of young Heralds.
It is awkward to write a review for a book you have not only read several times, but you have read the entire series to which it belongs. Separating your feelings for the characters and the writing becomes an exercise in futility. If you are interested in starting the Valdemar series, this is not a bad place to begin, and as long as you are content with a fun romp through a fantasy universe centered on magical horses and coming-of-age stories, you'll probably quite enjoy it.