Stop after this book if you want to discontinue the series. It does have a more natural ending than the others. The author does plan to keep going with it though, so if you like it, by all means, carry on.

The group is haunted by the things they have seen and experienced, the death, the horrible humans they have come across, and their resulting skepticism, along with the relentless cold and snow... The situation they are in is taking its toll.

Along with the 3rd book, there is a continuing grittiness and desperation. I feel like books 1&2 should have been combined, and 3&4. This is also quite short, but fast-paced. In book 3, there was more of a focus on horrible humans than the things in the darkness which I missed. In book 4, they made more of a return.