As frightening as the original miniseries was, I'm not sure if anything else will be able to scare me as much, but hey, you never know!
Warner Brothers has commissioned screenwriter David Kajganich to turn the story into one film, and he recently talked about his process of taking this detailed, long book into a single movie:
"In all of my talks with the studio, it has only ever been discussed as a single feature film. The book's length is clearly more suited to a mini-series and I understand very well why they went that route the last time around, but I think the book's content is really more appropriate for cinema. I told the studio from the beginning that I felt I needed to be able to write for an R rating, since I wanted to be as candid as the novel about the terrible things the characters go through as kids. They agreed and off I went. I think the biggest difference is that we're working with about two-thirds the onscreen time they had for the miniseries. That sounds dire, I know, but it doesn't necessarily mean two-thirds the amount of story. I'm finding as many ways as I can to make certain scenes redundant by deepening and doubling others. To me, this is an interesting process because it has the effect of thematically intensifying the whole, but it can lead to dramatic surprises. Certain scenes I thought would be crucial to the coherence of the whole ended up cut, while other scenes, which were somewhat cursory in the book, ended up being pivotal in the script."
So it seems that the horrible Pennywise the Clown will be making a reappearance to scare the crap out of us once again! And personally I'd love to see it happen!