SPOILER ALERT!
THIS IS THE END OF THE MOVIE!
I have my own take on the very last shot.
That take is: Christopher Nolan's kind of a dick.
Cobb and Ariadne wash up on a beach. The world Cobb and his wife built is collapsing. That's what happens when you build a world out of sandcastles.
~And if she asks you why, you can tell her that I told you that I'm tired of castles in the air...~
Gene soldiers are closing in on Eames, so he gives a gun to the dying man to protect the dead man with. This would make a lot less sense if they hadn't explained a whole lot of shit through the course of the movie, without too many infodump scenes, to boot!
Apparently, Arthur's not going to use the elevator's motors to simulate gravity. In the real world, the plan wouldn't work because the winches require gravity. He's going to use the kinetic force of the explosives. Okay. No problem.
"Listen, there's something you should know about me... about inception."
But instead of finding out what it is, we're back watching Eames get in a fist fight. Okay, I realize all this is taking place simulaneously, but time dilation effects and mumbo-jumbo.
Hey, come to think of it, why is the time dilation exponential? Only the first level should have a time dilation effect. Going deeper into your dreams doesn't make your brain work even faster. Dammit, now I'm going to have that bugging me the whole rest of the movie.
Anyway, Cobb starts explaining the memetic nature of ideas, which is kind of redundant for me to say, because the term "memetic" comes from someone trying to explain the nature of ideas.
Aha! Cobb thinks he accidentally caused his wife to commit suicide by planting the idea that the world was unreal. Of course, there's also the possibility that it was true and all of this is actually her performing extraction after extraction to try to get him out of that dream world. Somewhere, Cobb's in a coma and his wife keeps jacking in to try to wake his silly ass up and now I'm thinking of The Thirteenth Floor and that's not that bad a movie either except for a couple of places where it kind of is.
Except dream-wife (I want to put her name, but it kind of bugs me that the subtitles call her Mal but it's the only thing Di Caprio is pronouncing with an accent, so it comes out Moll) wants him to stay in Limbo forever.
And suspense action chasey chasey shooty shooty get back to the plot, dammit, I know there's shit going on in the other levels, but all that shit is incidental at this point.
Cobb confirms what I said a couple of paragraphs ago about him creating the idea that killed Mal (fuck it, if that's what the subtitles say, that's what I'll use). He did it deliberately, but it propogated up layer after layer.
The train kills them in Limbo, they wake up in reality, and she continues to follow the idea he planted (by spinning the top).
Van is falling. Time is running out. Shooty shooty splodey splodey. Saito "dies" which means he should wash up on shore soon too.
Music starts again, meaning another kick is coming.
Eames defibs Fischer, but the first jolt doesn't work because you don't defib a flatline but this is a dream, so I can let it slide.
Cobb rejects the projection of Mal. Ariadne kicks Fischer out the window just as the defib works.
Fischer heads for the vault with the hospital bed, just as Arthur triggers the explosive...
Fischer Sr. plants the seed: "I was disappointed that you tried [to be me]." The plan looks promising. The will is in the safe, the idea is there, Fischer is crying there's the pinwheel its all coming together it hurts it hurts it hurts ithurtsithurtsithurts
Hahahaha I kid.
The van hits, Limbo starts tearing itself apart, Eames blows charges...
Everyone's up to the top layer of dream except Saito and Cobb. Cobb finally says goodbye to Mal, letting her rest in peace or whatever SPOILER ALERT IT'S NOT REALLY HER IT'S HIS MEMORY OF HER.
Fischer pulls his "godfather" (Eames) out of the van, and proves the inception worked by stating that he's going to be his own man.
Now we're back at the beginning. And we find out that the pagoda with the old man is within limbo. Old!Saito reaches for the gun, and then Cobb is waking up in the plane. Everyone's happy. They've pulled it off.
It's time for the twist ending, methinks. Cobb meets up with Alfred Michael Caine his Father-in-Law. Cobb's kids are outside and there's the top spinning on the table, and it's spinning and spinning and spinning and occasionally wobbling and yes, it cuts to black just as the wobble intensifies because Christopher Nolan's a dick.
My conclusion: This is an excellent movie and there are plenty of clues supporting the theory that it's still a dream, but Christopher Nolan's kind of a dick, so I bet even if I had director's commentary, he'd be all "make up your own mind! (~theramins~)"