Odd that this thread was started in 2001, since I have 2 movies from 2001 to add to the list:
Planet of the Apes: I was going along with the whole thing until they got to the end, and then I was questioning EVERYTHING I saw before and wondering how they got to the ending from that.
AI: Good up until Haley Joel Osment goes underwater. The last part with him in the future getting his adopted mom back seemed completely different from the rest of the movie in terms of mood and plot that it looked like Spielberg tacked that onto Kubrick's original story.
