I think it's the execution that's the issue. splitting the book between John's story and the rest of the Lanterns was a novel (even ambitious) idea but it didn't really give what it was supposed to give. ultimately I feel it made both stories feel awkwardly paced, half-baked, and at points made some fans feel like John's story was a back-up in a book he was supposedly headlining. personally I didn't mind the inclusion of the new Lanterns (hell i didn't really mind the two storyline concept most times ) because contrary to popular belief GL is an ensemble cast/brand so multiple Lanterns comes with the territory, but there are more skillful ways than others to balance that ensemble element out. I think thats why some people are dissatisfied.
it also probably didn't help that a lot of people hoped for a more human John story to flesh him out as a person once he got his shot to headline and this run shoved him further into space/cosmic weirdness with little room left over for that groundedness people were looking for; due to the split storylines. however, the reception I've seen has been mixed, which just means it's one of those runs that wasn't for everyone. let's just hope DC doesn't bump John off so someone else can headline and allows more tie for John to be worked one whether it's under Thorne or someone else.