Let me first address all the negative reviews..

Rating: 9/10 (16 September 2019)

..because they all seem to have the same complaints:
1.) The Runtime:
Okay, you knew going in that this movie was 2 hours and 49 minutes, and if you didn't think a movie like IT needs such a long run time, you're clearly not a fan. The book is 1,200 pages long, and the first movie was 2 hours long and only covered half the story, so 3 hour run time for the second half of the story is more than justified. Yes, it feels long. But never are you bored. I will admit it does drag a bit in the middle, but that's mostly because the beginning was so fast paced. And they still left out subplots from the book, so it could've easily been longer!!
2.) The Comedy:
This film has no more comedy than Chapter One, and that was a highlight for people when it came to the first film, so not sure why it's such a drawback here. I don't know when comedy in a horror movie became such a negative factor for most people. Richie's whole character is a comedian who does impressions, and they're all childhood best friends, i'm Impressed that these friends can still find time to have fun after all the trauma they've been through.
3.) The Lack of Pennywise:
This is such a stupid complaint for many reasons. Pennywise is one of It's many forms, and let me tell you this movie includes much more of Pennywise than the miniseries, or the book. Had the ending stayed closer to the book, he'd be in it even less! But they found a way to include him and we should all be thankful. He is in it less than Chapter One but like I said, this movie isn't about a killer clown, it's about a shapeshifting entity that eats children and likes the taste of fear.
4.) Too many flashbacks:
Okay. The kids are not in this film as much as some people seem to believe. There's one flashback for each loser, and that's about it. This is the part of the movie where it starts to drag, but they're all relevant to the film as they have to remember things that we the audience didn't see in Chapter One.
Some people want this film to be closer to the book, but if it was, most people's complaints would be amplified, like a longer run time, less Pennywise, etc. Clearly there's just no pleasing people. Don't listen to the naysayers, Chapter Two is a much more satisfying conclusion than the second half of the miniseries was. I don't think it'll be remembered as well as Chapter One, but most of the problems in this film exist in the miniseries and therefore come from the source material. They would have to seriously detour from the book to please everyone. This one covers more from the book than the miniseries while also giving us something entirely new. You can tell how much Andy Muschietti appreciates and understands the source material, and that's rare. The director of the miniseries hadn't even read the book, and it shows. The miniseries May be a more faithful adaptation, but so is Stephen King's The Shining from 1997, and we still remember Kubrick's film.