Firstly, I'm a huge fan of the book, so when I saw this I was so excited to give it a go. My main positives are the actors for Tiffy, Leon, Holly and Mo - although not how I imagined them in the book, I really liked how the characters were acted. Justin was acted great and exactly how I pictured him!
I think my disappointments come a lot more from the storytelling, while I understand things need to be condensed for a show adaption it feels like so much was changed, packed in and rushed - it didn't give the same feel as the book. (Spoilers) Holly's death felt thrown in, Ritchie's appeal was rushed to one episode as Maia (should have kept Gerty) took the case the same episode. Was a shame how Racheal's character was changed since they're so close in the book and she's a great character.
A lot of the point of Tiffy's story in the book was overcoming her relationship with Justin and realising she was being mentally abused, it's a shame this was only really shown in the last episode and was overcome almost immediately, there wasn't a journey we got to see of Tiffy coming to the realisation Justin was no good for her. It also felt her whole dynamic with her friends was lost in this, as it's a main pull in the book.
Overall there were moments I did enjoy, I think you may enjoy this a lot more had you not read the book beforehand - as I have a lot to compare it to! It's just a struggle for me to get over the storyline, as I felt even with the changes it could have been written a lot better. Glad I gave it a go though!