- The part Shyamalan has chosen to cast himself in. Shyamalan's actually fine in it, especially given that there's an opportunity for the character to be relentlessly overacted and overdone--he resists that. However, by casting himself in the role, he's made the movie "about him." As Adam pointed out, this decision is on the level of Mel Gibson deciding to cast himself as Jesus. It's a killer.
- Just as significantly, the "villain" of the piece is (I'm not making this up) a movie critic who "doesn't understand the message!" Of course, this is made worse by the fact that the character is given supposedly witty things to say and comment on the action, turning it into an utter mess of commentary on commentary on commentary. My head hurts.
What's ironic is that the excerpts I've read from Michael Bamberger's book on the making of the movie all indicate that had Shyamalan listened to the folks at Disney, he would have had a much better movie. Sadly for all of us, he didn't.