More Fucked-Up-Coming-of-Age than Monster-Movie-Slasher-Horror. Which is what it should be, but perhaps not what it's marketed to be. Stephen King's It is one of my all time favourite books, and I don't know that it will ever get a faithful adaptation (totally understandable seeing as the thing is 1200 pages and contains a multi-book spanning mythology of Space Gods and Turtle vomit), but this does a pretty good job of interpreting the feeling of the novel, even if it's not a great adaptation the events as a whole.
The kids are all great, Skarsgård makes for a good Pennywise, Pennywise improves as the piece moves forward, and the town is completely believable as "Derry" in the '80s. It may not be all it's purported to be, but is a very impressive film on its own merits.
Final rating:★★★½ - I really liked it. Would strongly recommend you give it your time.