I really enjoyed the first book, I haven't gotten to the sequels yet.
The story is driven very much by the tension, the fear of what may happen, the almost pure evil of the villians of the piece.
The premise is "cute", that a certain few people can read out loud and people or objects from the stories will appear in the "real" world. And of course, one of the most evil characters ever gets read into life, and begins terrorizing the reader and his family.
The ending has some spectacular effects, and sadly this is what will be used in the trailers to sell the movie. The story itself isn't really a special effects story, it needs very little.
If they market the movie with the huge monster at the end, it will flop, because the story isn't really about that.