Its very good so far.. and yeah they plan to go back to other events where IT kind of resurfaces. You can tell they are making a universe out of Kings work, which makes sense because a lot of his books tie together in many ways.
For instance, and this isnt a spoiler really.. but they introduce you to Dick Halloran early on, who many will know as the hotel chef in The Shining (both movies and book). Hes actually a character in "It". So its pretty cool to see them trying all this together. And theres some real tear-jerking moments and also get out of your seat and cheer moments, too. It was pretty great IMO.