I can tell A LOT of you have not read the book!
1) In the book a lot of things are not portrayed in ANY IT movie.
Towards the end and after they kill Pennywise the first time; when the kids are trying to get out of the sewer they do something... something that is just messed up and doesn't make sense (iykyk) And that is not in ANY movie.
2) At the beginning of the book (i think) how Pennywise first comes to earth. That never gets mentioned anytime in the movies... (actually maybe the first movie in the 80s, Mike Hanlon might have mentioned it
3) In the book and the newest IT remake Stephan King talks about how Derry is a dark place and bad things just happen. It's not always a clown that does it however Pennywise feeds off fear so he's going to portray what scares people the most and it's not always a clown.
Great series so far