I started the series about a week ago and just finished them last night. I was hooked by the first one but also thought they got progressively worse.
They were definitely riveting, but I thought the author could have done a lot more with them. I feel like the content was too mature for the writing style. I wish the author had done more to create a more believable story without expecting the audience to take everything at face value. Maybe relied less on gore for the shock factor. Also, this may have just been my copy (I read an electronic one), but there were enough spelling/grammatical errors in the first book for it to be distracting.
I hated the ending of the third book. For me, there was no sense of resolution or emotional closure.
That being said, the series was a good break from all the heavy reading for school. I will be watching the movie.