Someone posted this about Inception on Livejournal.
While we were watching an inception being performed on the screen, Nolan was performing an inception on our minds. From the very beginning of the movie (once Cobb begins to explain the dangers between reality and the dream world), Nolan has planted the notion in your mind, through Leo’s character, that it was all going to end up being a dream. So by the time the end comes around, you’re like, “Well, yeah! I knew that was going to happen!” But you only “knew” because it had been put there.
Remember how Arthur says, “If I tell you not to think about elephants, what are you thinking about?” This mind fuck is much like this except it was presented to us directly. It was slipped in smoothly so, much like a parasite (as Cobb describes), that thought grew in our minds. This is why many have deemed Inception as “predictable”. In all honesty, though, I believe Nolan wanted us to think it was all a dream, thus distracting us from the fact that it was reality. His intention wasn’t to end it all as a dream. His intention was to make us THINK it all ended in a dream.”
I don’t KNOW what the truth about the story is but when the movie ended, I was convinced Cobb’s back in reality.