He captured the essence of the novel while making mostly surface level changes. My only real gripe is him giving Ben too much of Mike's role. Turned a fully fleshed out black character into a token. Made up for it in Chapter 2.
The show is pretty good.

There is no “It: Welcime to Derry” novel. This is a prequel.
I wasn’t that impressed by the series, though.
If you can’t say something nice, say something clever but devastating.