It

From the beginning of the book, with every character getting a hundred pages of introduction (even the 2 pre-murders in Derry), throughout it and to the end, it's the same convoluted mess. There is million of random characters getting chapters about themselves, even though you know they will be killed by the end of it. There is a lot of random philosophy moments (which I actually liked, but feel like there was A LOT of them and they kinda take you away from the story).
Main characters are interesting (a bit), especially the way we get to learn about them (through their introspection and flashbacks). But, I wanted to know more about them. Their whole stories in the novel were mostly about growing up, getting back to childhood, falling into same old habits.. I get that it's the theme of the book, but i feel like it didn't give a lot of room for character exploration.
I also liked side-characters (Henry Bowers & co, Tom, Audra...), although they weren't characterized a lot, except Henry and Patrick.
King's style of writing is great, as always - it creeps you out, it laughs you, it makes you sad, it makes you angry.... The way he writes those creepy scenes (e.g. Stan's introductory chapter) is really exceptional. I also like the structure of the novel.

To summarize, I enjoyed a lot of this book: creepy scenes, character moments (insights into Henry's and Patrick's psyche were great), some interesting visual descriptions.... But, it was too long, and there was a lot of unnecessary material.