I don't think the film earns a "punch in the gut" ending. I feel the tone of the film requires a denouement. For all the talk of Inception being a "mindfuck" film, I didn't think it was at all. I thought everything in the film was clearly laid out, everything flowed perfectly smoothly, and at no point did I feel confused or wonder what was going on or feel like I was being led to believe something that wasn't genuine and earnest.
That's true. Being a film about invading dreams and a purported 'mindfuck' I expected Inception to be a lot harder to follow then it really was. Honestly, outside of the first five or so minutes (that include an abrupt cut through time); I found the film pretty straightforward for the entire viewing. The only concrete subversive touch is the ending, but that the suggested dreamlike nature is telegraphed for us.
Any other interpretation I've thrown at the movie so far doesn't really stick (by which I mean 'oh maybe this
was a dream too or it's all a dream, dude
). Might be unimaginativeness on my part but this is by and large as straightforward as mind/reality films as they come. And that's really ensured by the existence of multiple perspectives. When you remove a film from a strictly subjective standpoint you begin to have frames of reference for reality to work with. Tell this entire film from Cobb's perspective and the whole thing might be fairly ambiguous.