I believe the "neutral" reviews are from reviewers not knowing how to feel about the movie. Strong feelings of pain from recollecting the day doesn't make anyone want to say they "loved it", in spite of how well it was made. At least that's the way it was for me This film was really difficult to rate in that it was a horrible experience, but that was what it was supposed to be. This was an amazingly crafted film. The use of no name actors, not making extreme characters (keeping them real), and personal camera work make the film feel very real. So real in fact that I experienced most of the same feelings that came over me on 9/11 and those feelings stuck with me for several days afterward.
If anything see the film so as to Never Forget.