Despite having read the Vampire Academy series awhile ago, I was still struck by the number of similarities between Half-Blood and VA. How did a publisher not catch this? Not only does Half-Blood include much of the basis for the VA series, but it also includes particular scenes scattered throughout the series! I understand nothing can ever truly be original after centuries upon centuries of storytelling, but how the hell did this get published? I'm not generally one who is bothered by similarities from story to store because of the aforementioned, but Half-Blood contained entirely too many situations for it to be a coincidence.
The characters in Half-Blood were easily interchangeable with VA characters, you simply had to insert their names and you felt like you were reading VA again (sorta, since VA flows better). The majority of the time I could not even remember that I WASN'T reading about vampires versus children of gods. There were so few differences I thought they had to be vampires, especially considering the neck biting and everything.
Specific similarities include the relationship between Alex and Aidan (holy crap! level of similarity), the training between the two, the covenant a.k.a. academy, relationship rules, a dear character turned into a bad guy that key player then has to hunt (seriously?), the love interest being made fun of for his reading of books in the training room (WTF?), and it goes on and on. I have never seen a book so clearly taken from another author!
Half-Blood starts moving away a bit from the VA storyline near the end, but I'd say 2/3 of the book was FAR too close for comfort. My recommendation is to read the VA series, it is done better and the main character is tougher and more mature.