Well the trailer looks bad still does even with context much better scenes to choose in the movie to tease. Overall I get why the reviews are bad, but it is like a Stephen King easter egg fest. They pulled ideas from most of the book and a bit of semi side stories, then within the movie itself you have a lot of Stephen King related stuff popping up. However the movie introduces a ton of things that never really get explained. could have used much more back story on Roland. Also very disappointing ending and a few things about Roland that I was not a fan of, but Elba was good.
Edit: Also the late reshoots is usually never a good sign for a movie one of the reason I expected it to be bad. You hear they see a cut it so bad you got to refilm not good. Going in with low expectations probably helped, but it is looking to flop hard so we will not be seeing more anytime soon if that happens.