Overly Convoluted, No Emotional Investment in Characters/Plot A corporate billionaire wants to eliminate his competition by implanting an idea in the subconscious of the man who stands to inherit the fortune, that he should dismantle the company into smaller entities. He hires Cobb (DiCaprio) to do this, who enlists a team. They tether together in dreams through a low-tech contraption that is never explained, which also puts them to sleep instantly.
To implant this idea in the man's mind, they have to go very deep, a dream within a dream, within a dream, within a dream. Down three layers. In each successive layer time speeds up so that hours in layer three is a few minutes in layer two, and seconds in layer one. To go three layers deep they need to take a sedative that is specially designed to deaden everything but the inner ear, so that the feeling of free-fall (called a KICK) will cause the subject to wake up. But one catch: using the sedative, if they die in the dream, their mind goes to "limbo" in real life, apparently a coma-like state.
They need about 10 hours to accomplish their task. Luckily for them, the target (the billionaire's son) takes a plane from Paris to LA regularly, and the flight is 10 hours. Arrangements are made so the private jet has mechanical problems forcing the target to take a commercial jet. To ensure they won't be disturbed in first class, the billionaire who hatched this plan buys the airline "because it seemed neater."
The dreamers carry their own talisman that reveals to the dreamer if they are awake or dreaming. Cobb has a small top that spins infinitely while dreaming, but in waking state it eventually topples. (How the other talismans work is never explained. Arthur has a loaded dye and the girl makes a chess-like piece. We never see them use theirs to check their state of reality, but Cobb uses his twice.)
The details of how lucid dreaming works is conveniently concocted for the film. One of the dreamers constructs a world in the form of a maze for everyone else to use as the dreamscape. The subconscious mind of the target fills the landscape with their unguarded thoughts, allowing someone to steal their thoughts (or plant a thought). A dreamer can also introduce fears and guilt into the landscape which materialize as threats, buildings crumbling, etc.
Cobb doesn't tell his team that he is deeply conflicted about planting a thought (inception) in his wife's mind, which was to question her reality. He did this while they lucid-dreamed together, which became an addiction, gradually revealed throughout the film as backstory. She finally jumped out a window to kill herself and wanted him to commit suicide with her, so before she jumped, she sent a letter to her lawyer saying her husband wanted her dead. Knowing he would get blamed for her suicidal jump, he fled the country to Paris and the entire movie takes place abroad. His drive to help the billionaire is a promised call 'to the right people' that will allow him to return home to be reunited with his two children. Cobb's guilty subconscious kept bringing his dead wife into the dreamscapes where she tries to kill others.
The dream sequences themselves are long, drawn out, convoluted, and often boring. They try to distract you from this by having constant gunfire from "projections" that are nearly always attacking the main characters. The villain of the movie was psychological: Cobb's inner struggle. That was a major weakness because there was nothing to root against. And you don't care about the main objective either (the billionaire's plan) – in fact the target is a more appealing character than anyone else in the film. So the only reason to sit through the entire movie is to see if Cobb gets to go home in the end, and frankly it takes the entire movie (if you don't walk out) to care about that too. And by then the only reason you care is b/c you sat through 2.5 hrs to see how it ends.
The best scene, dramatically, is when they wake on the plane and each look at one another after going through so much (~2hrs worth!) in dream state. The billionaire makes a phone call as the plane lands in LA, and Cobb clears customs. He is met by his Father (or his ex wife's father?) who takes him home. Cobb walks into the house, sees his children playing outside (as we have seen in many sequences throughout the movie) but this time he calls their names, and they turn around and look at him. At the same time he drops his bags, and as a last action, takes out his talisman and spins in on the table, then rushes to greet his kids. We hold on it in foreground while he picks up his children in background.... zooming in on the spinning talisman until it occupies the entire screen.... spinning, spinning spinning.... it starts to wobble ever so slightly... and CUT TO BLACK. Leaving viewers unsure if Cobb was still dreaming.
The ending was good and there were two other noteworthy scenes. One is a fight scene in zero gravity in dream layer two, and another was in the movie trailer: the dreamscape curling in on itself to form a cube.
Unfortunately, I didn't care about any of the characters nor was there any emotional investment in the main plot. Who cares if a billionaire gets his competition to breakdown his empire? And I also didn't care much if Cobb was reunited with his kids, as there is one lone scene of a phone call he makes to them that is supposed to establish our emotional investment, and it fell way short of doing that. Finally, as previously stated, there is no villain except for Cobb's guilt over his wife's death. I struggled to sit through this film.