These books are extremely addictive and completely satisfying... I only picked up the first one because we were on holidays and they didn't have what I was looking for... I hadn't heard anything about them, and was under the impression that they were mild thrillers... I was wrong, that first book is pretty intense and after reading the last 300 pages in one sitting I had the most intense night horrors ever!
The best two books weren't as damaging, but still all I thought about for the few weeks it took to read them... If you have some time, you should definitely pick them up... My only words of advice would be to make sure you have next next one ready!