Is IT the greatest horror movie of all time? Yes.

Rating: 10/10 (19 September 2017)

More than just a horror movie in the same way Pan's Labyrinth is. However, It breaks all the rules of slasher/monster flicks. IT gets away with revealing the source of evil in the first scene of the movie, and continuing to have scary encounters with the same source of evil, over and over.
The character development of the "losers" is as good as it gets. Personally, I felt as if I was one of the children, living in the time period, and getting into all the shenanigans young teens get into. The connection between the viewer and the children is profound.
The scary scenes possibly could be scarier, some might say, but I found them leaps and bounds over the typical scares of even good horror flicks. There are no cheap thrills. All scares are legitimate. No camera trick scares, like an innocuous character lurking behind a door and a big musical overture just to reveal nothing actually scary.
The score of the movie was perfect. The music told you how you should be feeling but wasn't too hyperbolic at scary parts.
There were some things that you had to overlook, like how the kids were finding murder evidence and not reporting it to the authorities, but that just added to the theme of childhood hubris. In the horror genre, typically, there are dozens of small things and inconsistencies the view must overlook. That isn't the case with IT.
The directorial decisions of what to keep in the movie all flowed well. Everything made sense in the end, from the pennywise personalized scares for each of the "Losers", to the strong relationship and character building. Perfectly executed, and the movie's length is exactly what it should be. Any longer would be too long, and any shorter would leave out key moments critical to character/relationship development.
I watched very few movies as a kid that absolutely scared the crap out of me, The Shining being one of them. I can't imagine watching IT as a 12 year old at home alone like I did with The Shining. IT is going to be giving children nightmares for decades to come.
Without revealing too much, I will say that there are no movies in the genre of horror to compare this too, perhaps Pan's Labyrinth (as stated before), but that is a stretch. JUST WATCH "IT" ALREADY! Definitely a must to see in theaters.