I haven't seen the new IT movie, but I've heard good things. However, I don't see the second one being good at all. Why? Simple, IT was based off of a book by Stephen King. The old movie was good because of it. I don't know what they did for the new one, but being based off the book, I can assume that's the reason for its success. I don't think Hollywood can strike gold twice with a sequel that's not based off a book. Unless they have Stephen King help write it.
Plus, I hate unnecessary cash grabs on movies because of the name. It's why I refuse to watch The Hobbit. I read the book before the movies came out and the fact there's three movies for a book that's only a few hundred pages long is disgusting. It's not like LotR that has three books. Plus, I saw the first quarter of the first Hobbit movie and it was annoyingly bad. That's what I expect of the sequel. Just plain bad.