I went into detail in my "IT (2017)" review about how this was my first horror movie (well, first I attempted, not first seen all the way through) and how it scared me for years and how nostalgic I am etc etc. So I'll get right to the point. The 1990 miniseries is far from perfect, and one of the few horror movies where I can say that the remake is better in almost every way. If you haven't seen either, go see the remake. Actually, read the book, then see the remake. Hell, by the time you finish all that, part 2 of the remake should be out!
On to "IT (1990)". Like practically everyone will tell you, the movie shines in the first half. The setting of Derry is imagined well from the pages of the book, given even more life by the child actors. I really liked this group and they captured the feeling of being outcasts well. They feel like your friends as well as eachothers. It's a strong theme of the first half that, like everything else, the second half doesn't pull off nearly as well. The main attraction though is Tim Curry as the titular IT, or Pennywise as his clown form is known. He can take on various guises, but the clown is who you'll remember. And that is because Tim Curry is as awesome as he is terrifying. He even carries the weaker second half entirely on his shoulders.
I know where the films scares are now, but the infamous Georgie scene still gets me. Luckily it's right at the start so i can relax a bit more after it, but there are still fun scares dotted throughout. Whether this movie will scare you depends, as I've had as many people tell me they found it daft as people that shared stories of sleepless nights due to it. I fully admit it's mostly a fun, nostalgic trip for me. Without that, I'd still recommend it, but there are much better horror films (hint: one with the same title).