Let's start at the end. Inception's ending is perfect.
If the top had stopped spinning, we would have been disappointed. If it had kept spinning with perfect, uniform grace, we would have been disappointed. The final frames of the film, which linger just long enough to provide us with doubt as to the top's fate - one way or the other - is perfect.
If it had ended any other way, we wouldn't want to talk about it afterward. But it didn't end in those two other ways - and so you've got to find someone who saw the movie and talk about it. It didn't explain itself - it expects us to explain it to each other, and argue over which of us is right.
Inception is a great show, but to draw analogy to video games, it's more great in the way Uncharted 2 is great, not Demon's Souls. Yes, the artistry is there - but what makes Inception largely above par is its collection of exemplary strengths: great cast, great writing, great plot, great cinematography - another great movie from Christopher Nolan.
Outwardly, it's a good action movie. You can go into it with a limited attention span and still enjoy yourself, without worrying about the high-concept science and psychological fiction being explored, here.
What makes it great is the rest of it. The stuff you want to talk about afterward - which I'm about to discuss...
He's still dreaming. The whole thing was DiCaprio's dream. How can one be so sure?
First off, there's the repeat appearances of his wife whenever he enters someone else's dream. When DiCaprio is training Ellen Page to construct a dream world by allow her to enter his dreams, he explains that the world is populated by aspects of his own subconscious - the other people in the dream are "like white blood cells," he says - and they'll attack her if she fucks with the place too much.
Likewise, when they enter someone else's dream, that dream is populated by the host's subconscious.
Except DiCaprio's wife keeps showing up and going crazy - in everyone else's dreams. Why isn't some aspect of Ellen Page's subconscious pulling crap? What about Joseph Gordon-Levitt's? A guy that straight-laced has got to have some awesome demons, deep down inside. But no, the only violation of this rule is Mrs. DiCaprio. Why? Because DiCaprio isn't actually going into anyone else's dreams - he's dreaming that he's going into other folks dreams, and because it's still his dream, Mrs DiCaprio shows up to wreck shit.
* * *
The other pointer is the rules that are set up regarding how one accesses "Limbo" - or this state of eternal consciousness at the deepest, darkest depths of one's dreams - and therefor, how one leaves it.
First, there's a dream. Beneath that is the dream within a dream. Beneath that is a dream within a dream within a dream, and if you dream in that dream, bam - you're in Limbo. To wake up from a dream and climb back up on the dream-ladder, you have to a) get killed in the dream you're currently in or b) be "kicked" (tipped over) in a higher-level dream or, finally, reality.
That, or some unexplained crap about drugs.
Now, DiCaprio was in Limbo with his wife. He convinced her they had to return to the "real" world, so they laid down with their heads on a train track to wake from that dream within a dream within a dream (within a dream).
...which still puts him three dream-levels in.
But if those rules actually apply, doesn't that mean DiCaprio would go straight to Limbo the first time he started to dream within his current state of third-dream-level?
What the fuck?
Inception practically puts a gun to your head and demands you have this conversation with people.
Which brings us back to the top, and the top's fate. I find it rather delicious that I, and likely anyone who's seen the film, becomes so momentarily obsessed with discussing the truth of it - but while the top itself is what denies the audience the standard movie-goer release: the ability to walk away and forget about it - the ending is actually about DiCaprio's reaction to the top.
He starts it spinning, but doesn't wait to see what it does. His children turn their faces toward him, and it doesn't matter, he realizes, if this is a dream or not. He walks away, and doesn't look back to see the truth of his reality - he is free of it - but we, the audience, are chained to the need to know.