I absolutely love the book series! It's so well done. Overall, this is a great adaptation. I don't understand some of the choices (i.e. SQ is Curtain's son, Sticky's parents are dead and his aunt/uncle were the ones who had him on the trivia circuit), but overall not a big deal.
My two biggest issues: they made Kate annoying (I did not find her annoying in the books at all) and they made Mr. Benedict more anxious. It's been awhile since I read the first book, but I recently read the rest of the series. Kate was always confident and competent, but also a big team player. She's too arrogant and "maverick" in the show.
And Mr. Benedict is not portrayed as an anxious, nervous person in the books! He's certainly concerned for the children's safety, but he's confident in his plans and decisions. I pictured him more calm and confident than he's portrayed in the show.
Again, overall I really like it and think it's a good interpretation of the book. Those two things are really my only issues! Maybe they'll consider being more true to those characters in future season?