This isn't your typical shoujo, regardless of what other commentators would have you believe. There are going to be differing tastes when it comes to mixing genre's, in fact it's rarely done well. In the case of Akatsuki no Yona (AnY), it's succeeded in almost every way.
Let's start with the characters since they have been accused of being shoujo cut-outs. I couldn't disagree more, the characters are unique and very strong in their personalities. I consider bad character writing to be where a personality breaks its mold or tries to be everything to everyone. You see this in alot of shounen manga/anime, but in AnY, the characters are all very much different and fill their roles very well. What makes the characters especially good here, is that they all have solid and personal motivations that are believable. Almost every character wants something different even if they're paths align. The characters are also written almost morally ambiguous; in other words, there are no black and white, good and evil characters. This is far closer to reality. What one person considers evil, is often justified through subtle writing, whether you agree with their justifications or not. This is obvious with Su-won and Yona, I personally hate Su-Won but the dynamic between those two characters is refreshing. Su-won isn't a caricature written as a place holder of the evil bad guy. He has is own beliefs and ideals, even if they clash with the main character. That builds enormous tension and plays off the strength of the differing personalities. It creates so many dynamics between Hak, Su-Won and Yona and gives the story even more depth.
I would say, without a doubt, the character writing is this manga's strongest point and what makes it interesting. Even if this had a weak story / plot, the characters could pull it through. Fortunately, the story and setting are very interesting even if its been done before. If you were to criticize anything, it would have to be story. It's simplistic and relatively straight forward on one hand, and yet it's propped up by the interesting political schemes and world building the author juggles. It never really jumps in too deep, but it also doesn't resort to deus-ex-machina machinations either. This keeps it light and allows the reader to grasp the deep subtleties that are around every corner.
The reason this works is down to the pacing. So far the story hasn't stagnated at all, but moved briskly through the story while retaining alot of the mystery and intrigue that hooked you at volume 1. The best writers know how to keep you engaged through mystery by giving you what you want at the right moments, and AnY is no exception. What i dislike, probably the most, out of stories is seeing the end of a goalpost and being hand-fed clues to how it all ends. I have no idea how the author will resolve the most interesting bits of this story, and that is a good thing. The only draw back to this approach is that when building it up so much the resolution can often times not meet your expectations. So far though it has blown away my expectations and so i have high hopes for all the story weaving that this tapestry offers.
I don't want to pretend that AnY is a masterpiece of literature, but for me the most important element of manga is enjoyment. I've seen and read hundreds of anime/manga and its rare to come across something like AnY that keeps alot of the good elements of manga genre's and twists / plays with them in different and exciting ways. Not everyone is going to like a certain manga, and some people will absolutely not like the large combination of genre's that this offers, but when it's done right I think it transcends even manga that are masterpieces in their respective genres. Shoujo is definitely not my style, but it's appeal is reaches far beyond that. This is simply a good, fun read. And I hope you give it a chance because it has something for everyone.