Firstly, there was the issue of Dane. It is made very apparent that he is "bad" - but more because we are told this, than from being led to really feel this way. I found his rather sudden, violent attack on Jenna a surprise, and not a "wow, that was a significant plot-twist" sort of a surprise, but more of a "why exactly did that just happen?" moment.
Also, her relationship with Ethan seemed forced, like it was happening because that's what the author wanted to happen, rather than through the characters desires. There was no chemistry between them.
However, the story was captivating and thought-provoking enough to keep me hooked, and I would happily read it again. I'll probably read the sequel too, just to see what happens to her dead friends.