I want to believe that it was real. Otherwise, the whole movie is just about a guy taking a nap, and none of it matters.
Except that, even if stuff in the movie was "real," it still didn't really happen because, you know, it's a movie.
None of it matters except to the extent that all movies matter. The characters & events are as real & important as you want them to be.
Honestly, I have a hard time doing any literal analysis of this movie. When I do, too many things don't add up. But then, I think that a lot of Nolan's movies are like that. Analyzed literally, the Joker's clockwork perfect crime spree in The Dark Knight
makes no sense at all. The Joker must be analyzed as a symbolic force of chaos. And while the ending of The Dark Knight
seems very impractical & unnecessary on a literal level, that too makes more sense on a symbolic level.
On a symbolic, meta level, Inception
is about the process of artistic creation, manipulating the emotions & ideas of the audience. Just as The Prestige
was a movie about magicians that was itself a magic trick, relying on doubles, deception, & diversion.
It being a dream at the end pretty much makes Leo's character arc pointless, meaningless and depressing given that in 'reality' he's either going to eventually wake-up and not be with his kids and possibly still be a fugitive or he'll be a vegetable (given the rules laid out for spending too much time in Limbo/a dream state.)
Or the whole thing was a dream, and when he wakes up, he'll be in his bed next to his wife with his kids in the next room. Or maybe he's actually a woman who dreamt that she was Leonardo DiCaprio.
Or the entire movie was really dreamed up by that autistic kid from St. Elsewhere.
Considering how preposterous the technology in the film is and how it totally flies in the face of what the modern understanding of dreams is, I'm inclined to believe that the whole thing was a dream. There's no such thing as extraction, inception, or any other form of dream walking. None of these people ever existed; or if they did, there's no reason to believe that how they're depicted in the film bears any resemblance to "reality."
Which annoys me slightly if only because the implication is that Cobb is the only real thing in the entire movie and I think he's the least interesting character. I would have preferred a greater focus on Arthur and/or Ariadne.