This novel was very good up until the last novel.
I have only read it up until the 4th novel up until the 5th chapter since I do not have the Japanese novel and I am only reading an online translation that is still being translated, therefore my opinion will be based on that.
I love this novel a lot, the story was very nice and I love the idea of it... But, when Kyoto animation made the anime they changed the story completely.
Then the story started going downhill around Novel 3, but it was still okay.
My idea of it is that Torako did that because of the anime's story and the anime being praised more. Therefore they tried to adhere to the anime's story, but that didn't work, because the story is nothing like the anime.
Their story was better than the anime, so it is upsetting to see them doing this.
The novel is still better than the anime by far, but the 1st novel and 2nd novel are the best, because they were not influenced by the anime adaptation. (Since the anime hadn't come out until the 2nd novel was made?)
Dekomori seems very very very forced in the novel, which Torako said in the afterword of the 3rd novel, "Deko-chan’s appearance was quite forced though…"
Online, I see so many people say that they think the novel is bad because Dekomori isn't there, or Kumin, or Tooka.
Imagine being told that a horrible adaptation of your novel is better because they had 3 other characters added that were completely useless to the story. That's horrible.
His adaptation of Kumin was good in my opinion, but Dekomori was quite annoying. I might have a "biased" opinion on Dekomori, since I hate her in the anime too, and she hates Yuuta, which is my favorite character. But her personality is overall annoying.
I barely have any complaints for the 1st or 2nd novel. They were outstanding.