Not to disagree with the commentators who prefer the novel, but I don't think that this film is missing anything or doesn't make sense, as some claim. What parts would you rather see included? Maybe the part where
the children enter the sewers, Bill performs an ancient ritual that takes him into another dimension where he meets a giant turtle that created our universe by vomiting it up, which helps him defeat It and afterwards the children get lost in the sewers and Beverly has to have sex with each of the boys to "restore unity to the group?" Is that what you are missing?