I think this is a terrific meditation on 9/11.
The reviews listed below seem to focus on the fact that nothing "happens," but I think that's this film's power.
The crunching together of time/space; the visuals of pre-9/11 and the audio of post-9/11; it's as if the actual act of destruction is too much to handle. By sidestepping the event it makes it much more visible in the mind. Well done.