My favourite thing was the implication that Anne was regularly writing steamy letters to Gilbert.
I also liked Katherine and particularly

that she does not get her problems solved via marriage

.
The bullying in the first section was pretty tough to read about, as poor Anne has half the town against her and the rest too scared to do anything about it.
I also didn't enjoy the lengthy monologues by people just telling their random family histories etc. Please be a little bit relevant to the plot....

My rating scale, for reference:

 
I liked Anne as a character in this book. I liked the way she viewed the world, and I liked her optimism, her refusal to give up on even the most prickly of people, and the gift she had for lifting and brightening the lives of those around her.

I liked the setting of this book: Anne’s cozy tower room, the garden gate through which she spoke with little Elizabeth, the graveyard she walked through when she needed to think, the groves of trees, the red ribbon of road with white houses, the blue hill Anne nicknamed the Storm King, the blustery storms…

And I liked Montgomery’s poetic writing style, as always.

But plot wise? It pains me to say that this book was not very interesting. Sure, I enjoyed watching Anne (spoiler)

win over the Pringles (even if it was mostly their fear that she would reveal their “cannibalistic family secret” that won them over vs. her natural charm)

. And I enjoyed reading about her relationships with some of the people in Summerside, particularly Elizabeth, Katherine, the Aunts and Rebecca Dew. But otherwise, it was mostly a lot of talk and gossip of random people, sometimes through the lens of their relatives and distant relatives. Take this sentence from page 276, for example:

“There is an attractive Palmer girl who is reported to be throwing herself at his head, and his sister is said to have said that his mother has said that her son has no need to dangle for years at any girl's apron-string.”

If I don’t know or care about the first person you’re mentioning, I’m for sure not going to care about who they’re related to or how their multiple-removed connections think or feel about a situation. And this is what the bulk of the book seemed to consist of: little stand-alone / incoherent vignettes of Anne interacting with the locals in gossipy ways that I honestly didn’t find very compelling. This makes me feel sad, because this is Anne of Green Gables we're talking about! There’s so much childhood nostalgia wrapped up in the Anne stories for me, but I've found that the further away I've gotten from the original book, the more these books have felt rambly and full of convoluted connections and talk of people who were introduced on one page and then disappeared a few pages later.

And, apart from a few key people (like little Elizabeth), these superficial connections or interactions seemed to happen at the expense of any real connections. When Anne went home for visits to Green Gables, for example, we hardly heard anything about the people she’s loved her whole life. Marilla, Diana Barry, and her adopted younger siblings barely got a mention. Even Gilbert! It was weird because most of the book was written as letters to him (oddly, with any lovey-dovey bits redacted), but we didn’t get anything from his point of view, nor did we get any scenes of Anne and Gilbert together. And then when Anne left Summerside after 3 years of living there, it was only the people she was leaving behind that seemed to feel sad at her departure; Anne herself didn't really seem to care all that much. So the book was chalk-full of superficial connections but lacked the magic and depth of Anne's prior connections and friendships. 

Oh, Anne. I love you with all my heart, you are my happy place and you didn’t disappoint in this fourth book. I can’t wait to read the other four!

A large part of this book is various characters complaining or being grouchy. It gets a bit tiresome, In my opinion. My favorite parts of this book were the summers back in Avonlea