The first thing to note is that the Vampire Girl series is, to me, something akin to literary candy. It's enjoyable in a lot of ways, and you know there's some not-so-great-stuff that comes with it, but it's nice to have a taste all the same. I like a lot of the ideas in the series and appreciate the general tone, ethics, etc.--it's fun but not gross, entertaining but not soulless, toned down and simplified but overall well planned and executed, a sort of not-so-guilty guilty-pleasure-- but the reason this doesn't count for me as a serious fantasy or romance is that each installment is very short (around 200 pages) and everything unfolds at breakneck speed. I'm more for a moderator pacing that allows everything time to unfold--romances shouldn't be instant and explosive, secrets need to be set up for a shocking reveal, details need to be woven--but since I know this series is targeting a teenage demographic, was written in a more serial format, and kind of relies on the pacing to keep you interested with twists and action and plot development, I won't be too harsh on it.
That is kind of my whole criticism of this book and the previous one, and it will likely follow to the next two installments as well--it has a lot of wonderful ideas and an interesting story, but instead of taking a more traditional fantasy-romance path where it takes quite a few pages for everything to happen, things here are cut down to more of the basics so we move along through the major events very quickly. I can't tell if this is a deliberate choice so it appeals to a wider YA audience (though Arianna is 18) who maybe don't have the time or desire to commit to the heaviness that can come with fantasy by quickening the pace and cutting down the fluff to the details that are more desired (like the declarations of love, the attraction, the twists), or if the authors mastered a more simple style of telling fantasy and crafted a story to suit that.
Although one thing I did find really eye-roll-worthy was the fact that Arianna gets a baby dragon spirit thing and she's called its "mother" and I'm just over here like everyone and their grandma wants their heroine to be Daenerys Targaryen, don't they?