It's Christopher Nolan's best work ever, and Leonardo DiCaprio rocks in the movie. It's built on a unique and mind-blowing idea- that it is possible to take control of our as well as other people's dreams, extract information from the subconscious, and even plant new ideas.
Don Cobb, played by DiCaprio is hired by a business tycoon(Ken Watanabe) to get into his rival's subconscious and extract ideas. He is in his missions haunted by projections of his late wife(Marion Cotillard). Cobb is assisted by Arthur (Joseph Gordon-Levitt), Ariadne(Ellen Page), Tom Hardy (Eames), and Yusuf (Dileep Rao) in his mission.
I don't know about you, but I remember having dreams within dreams. Yes I was a strange kid. Anyways the same concept is developed into being able to dream in several levels(dreaming within a dream, in a dream while one's dreaming)- some might get a headache. The terminology introduced in the movie is awesome. You need a totem to tell the real world from a dream(you might get confused!). 5 minutes in the real world equals 1 hour in a dream, and the same conversion rate proceeds in subsequent levels.
It's meaningful to compare the movie with The Matrix and Avatar- we almost get the same thrills(or better). It's fast-paced, contain intricate detail(I couldn't grasp it all in one see) and might not fit into the mass audience for the same reason.
Nevertheless, watch the movie at least once. You get ones like this very rarely, don't miss'em.