*Plot spoilers below
Musings on the film in no particular order...
1) Too much time was spent expounding upon the rules which govern dreams. Rules should simply set up the story, not take the place of it. The rules are so intricate they require several scenes to explicate them.
2) The ambiguous ending co-opts the rest of the film. Audiences will be spending all their time debating what happened at the end instead of arguing about the film as a whole. This is a waste of time UNLESS the ending is essential to the overall theme. In which case, it is important to know how it ends. Or it could be that AMBIGUITY itself is the overall theme.
3) Thomas Hibbs argues in Arts of Darkness that there is a subset of films within American Noir which "characters engage in a kind of quest to recover something." Since these movies are a subset of Film Noir, they do not find what they're looking for, but movies avoid nihilism because the characters have "some sense of proper orientation; of not losing oneself."
Inception definitely falls into this category. Cobb wants to "recover" his children and spends the entire film trying to do so. In film's climax, Cobb is tempted to choose between living in a dream world or going home to his real kids. He orients himself correctly by picking reality. Yet in the final scene we are left with the possibility that his real kids are not real at all and that he is still stuck in a dream. Does this make the film nihilistic? Hibbs' argument is it can escape the nihilism charge even if Cobb does not make it back to his kids because he at least oriented himself correctly. He WANTS to return home. That he isn't there yet is another matter.
What happens to Hibbs' argument if Cobb is CERTAINLY trapped in a dream? I think Hibbs would say it is nihilist then because there has to be at least the possibility of a recovery.
Albert Camus, on the other hand, argued in the Myth of Sisyphus that meaning was still possible in such a situation: "The struggle itself...is enough to fill a man's heart. One must imagine Sisyphus happy." But this answer doesn't seem satisfying. It just sounds like playing pretend. And most of us lost that attitude when we grew up.
4) James Bowman, in an essay titled "Avatar and the Flight from Reality," uses recent films to show how ancients and (post) moderns view art's purpose. Ancients believed in the concept of 'mimesis', in which art is evaluated by how successfully it reflects or imitates reality. Postmoderns flip things around and make art the measuring stick for reality. Cobb and Mal created a dream so beautiful that Mal did not want to leave. Ariadne says what they're doing is "pure creation."
So did I like the film? Yes. Is it Nolan's best work? No. His worst reviewed film, The Prestige, is better. But then again, The Prestige was really good so that isn't a harsh criticism about Inception.