There are several reasons why:
This story has been done before. I knew what was going to happen before I was a quarter way through the book. (Now this might be because I've read most of Christine Feehan's Carpathian novels.)
What really made this book disappointing to me it that the character "Chris" did not feel like a guy to me. I had heard other reviewer refer to characters as "women in drag", but this was the first character that really came across like that. I really tried to remove that impression, but it was continually reinforced. The vampire even asks to call him Christopher instead of Chris.(Wonder Why???)
Maybe I've become cynical. Read it and see. I just couldn't believe in the Characters.