I probably would have enjoyed the book more if it didn't sell itself on the promise of a twist ending. I went into the book knowing to expect the plot twist, so when it did happen, instead of being surprised I just sort of shrugged and said, "Oh. So that's what it was."
I liked the idea of Cadence as an unreliable narrator, except she wasn't really all that unreliable. Everything was pretty straightforward, actually, so that by the time enough of Cadence's memories of Summer 15 had been laid out, I roughly knew what was going on with the rest of the Liars. She never really kept me guessing as to what was truth, and what was lies. And that was what I had been hoping for.
Even the Liars themselves weren't really liars. Unless that was another lie.
Gat was by far the most interesting character, even though he was an incredibly pretentious ass who repeatedly compared himself to Heathcliff from Wurthering Heights. Oh, did I get tired of the comparisons to Wurthering Heights.
He at least had his pretensiousness to rest on, though. Everybody else was just really rich and whiny. Seriously. The entire reason the plot twist happens is because the family is fighting over who gets what house when the patriarch of the family dies, while the patriarch jerks everybody around and turns each of his daughters against the others.
...there's also a lot of King Lear comparisons. Obviously.
Cadence also keeps rewriting the story as various fairy tales, as well. Because there's three daughters. In case you didn't catch that from the King Lear comparisons.
I actually liked the fairy tale bits the best. They're the reason I ended up enjoying the book as much as I did. But then, I'm a sucker for fairy tales.