It's a frustrating movie, it has a great concept, but Shyamalan didn't handle it too well. The movie is there, I don't know why it didn't add up, maybe it's the editing, the pace, the shift in tone...it's too suspenseful at times with no payoff...There's some great things in the film, and I recommend seeing it....
I am not the director, so I can't say it would be better if it did more of this, or less of that, etc, but when I see a movie and I can only think about what I would have done, I only think of that when a film is a disappointment.
I don't believe there is sch a thing as a bad idea, at least in art/film making, but the execution has to be right, or at least treated seriously by the artist, and I get the feeling that Shyamalan got too excited by his ideas in this film, but didn't care to explore them, I don't know...