left me with a hollow feeling.

While I have enjoyed all the books in the series, the fourth book (to me) feels more true to the original. Joe is just as psychotic, if not more. It does move much more slowly though, in comparison to the first three books. I can see many being disappointed because of that, and the lack of a certain type of ending, but I actually enjoy the break up of the usual pattern the past books have used. With that said, I have the feeling that this is going to feel like a two-part book and the upcoming book (who knows when, Kepnes only announced that she was working on it a few weeks ago) will tie up any loose ends and fix that feeling that this is incomplete/lacking.

It doesn't feel that way to me (incomplete, that is), and its ending angered me because Joe angers me and not because I felt anything lacking. I think this sort of hints at some changes in Joe from what he previously experienced. I'd go into details, but then I'd have to add spoiler tags and I just don't feel like doing that.

TLDR, I enjoyed it thoroughly and I will continue reading upcoming books in the series. Also, it is good to note that I read this with the audiobook, so Santino Fontana's narration likely skewed this for me a bit. He's just the perfect narrator for this series.