I think the best way to describe this series is "oppressive." It's like a talented painter is showing off a new painting, but the only colors used were black and slightly less darker black. I understand that to a large extent this was the intent, but without contrast it all just blurs together.
Basically, it is the opposite of a slice of life style, in that every scenario ends poorly for the characters. It becomes predictable in that you know every outcome will be bad. You might not know exactly what is going to happen to them, but you know it will be bad. The few times things seem good, you learn to expect that it's just a bait and switch. I can tell the author is talented, but it's smothered under an apparent need for all the bad things in life to happen to these characters.
This last book was a real struggle to get through. There were arcs that felt unnecessary and the ending is not satisfying enough to justify the experience.