There was an interview that I read, either with the show runner or Shyamalan, where it's mentioned that viewers will be surprised that one of the characters doesn't make it past the third episode. I'm guessing that would be the sheriff, who is killed at the end of the first book. So if this show is faithful to the books and maintains the same pace throughout the series, there's a strong possibility that the 10 episodes are going to cover the entire trilogy. Not a bad idea, really. The books, themselves, don't really contain a whole lot of dialogue between characters and is mostly written in POV style. A lot of filler would be needed to stretch one of the books past five episodes, at the most.
I, too, look forward to seeing what the creatures/abbies will look like, though I'm prepared to be let down. They were one of my favorite things in the book. Such mindless savagery. But there's also the female that's kept in captivity in the facility, who I wanted learn more about, since she seemed to be a more docile version of the species, with perhaps a measure of intelligence.
To say that Shyamalan probably dug the book's twist, would probably be an understatement. This is probably the most perfect of TV projects for him to have gotten involved in. I wonder if back in the day, back when he had more pull in Hollywood and wasn't as criticized, would he have decided instead to have made this into a movie.