The most rewarding part of watching such movies is the uncompromising way in which the movies force you to be involved, stay on top of things, think quickly, form theories, constantly correct them and in general live through an experience similar to what the characters in the movie seem to be experiencing. Its like a puzzle that gets harder and harder. Inception deals with the concept of placing a thought in a person's head with several levels of redirection. The planting of the idea must not be explicit but should appear as if the idea formed as a result of the person's experiences. These experiences happen in a dream. And the dream that is the genesis of the idea is a nested inside another dream, which in-turn is nested inside another dream. Dreams appear to be C program type loops and nested dreams follow the logic of nested loops, where for every iteration of the first loop there are N iterations in the 2nd order nested loop and N^2 iterations in the 3rd order nested loop. So 10 hours of sleep in the first loop translates to 50 years of life in the 3rd order dream. This concept is used superbly by characters who make up for time related short-comings by opening up a nested dream that buys them more time (30 minutes of the movie happens between the time it takes atruck to fall from a bridge into the water). There are rules and logic in the dream world, 'break' operations that can cause loop exits - called 'kick'.
Nolan hints at what is to come when the architect, Ariadne, who is tasked with architecting the look, location and feel of dream world, shows Cobb a sample of what she can do. In a classic moment she does with mirrors a image that resembles the classic picture of a man drawing a picture of a man drawing a picture of man drawing a picture... And we are not sure if we are part of the picture or outside it. Cobb thinks he is sure. But is he? The ending is just incidental to the overall movie experience. I cannot find words to describe what an experience it was watching Inception. This is true movie making of the highest calibre. Worth waiting 4 years to a get a movie that treats the audience with intellectual respect.