It’s funny- I totally agree with your negative points, but I still rather enjoyed the book. It was fun getting into Emma and Snow/Mary Margret’s heads. Most of your cons relate directly to your first point- that the stories are told from only 2 points of view so any moment they were not directly involved in gets only a passing mention. I was wondering how they were going to do that when I first heard they were doing it that way. I thought it was pretty clever to have Henry recount the other characters’ stories through his book, but yes- I missed having them fully fleshed out. They could have done a set of books instead of trying to squish the whole season into one.
I didn’t notice all of the dialogue changes because unlike many other Oncers, I haven’t actually gone back and rewatched earlier episodes! I did notice that Rumple never said “Dearie” which I thought was odd.
I think the book is at least worth a read for any Oncer. I would just recommend going in knowing it’s not an exact transcript of the show and accept it for what it is- a quickly produced and thrown together adaptation made to cash in on the popularity of the show . It’s fun to make comparisons. I agree that one should only read it if one is familiar with the series, or it might get awfully confusing.