Something that has bothered me is that the show has almost completely glossed over Jake's role as a teacher and the relationships he developed with the students. While it isn't super integral to the story, it was a big part of the book and it would've given Jake's character more depth.
I understand they probably wanted to give Jake a partner (Bill) because being alone doesn't make for great TV, but they could've focused on the teaching aspect more to overcome that. The whole Bill angle was just stupid. Stephen King was an executive producer for the show. I'm surprised he didn't shut that idea down.