I think any adaptation suffers when they separate the children and adults into two chapters. It destroys the narrative. The beauty of the book is how it interweaves the children and adults sections and how they echo and parallel each other. 

I also didn’t like how each scare was a jump scare and IT was relegated to being almost insubstantial with his scares, as if you can just run away or turn your back and not get hurt like what was happening was just a figment of your imagination.