I wonder if it's a coincidence or if directors just have a sense of humor, but I find it amusing that Leonardo DiCaprio's last two films have both begun with treacherous looking water. I don't think he'll ever escape Titanic. There are many more similarities between Inception and Shutter Island that are much more substantial, but we can talk about those once you've seen both films.

Inception is a typical one-last-job crime film--except not. It's a unique twist on the crooks-we-like film that audiences have come back to year after year. In order to return home to his two children Cobb (DiCaprio) accepts the assignment of a Japanese businessman. Instead of extracting secrets from people's dreams, which is Cobb's normal line of illegal work, for this job he is asked to incept--or plant--an idea, which may or may not be possible. For this kind of sci-fi thriller to succeed the film must firmly establish the rules of the world, which is an interesting challenge for this film because what kind of rules are there in the dream world? Somehow Nolan manges, again, to bring his audience into an adventure that is believable but shockingly imaginative. He capitalizes on the common experience of dreaming--common to all, but intensely personal as only you can experience your own dreams. The film deals with shared dreams, achieved through some mechanical/chemical process, and thus includes dream elements that everyone can relate to: the feeling of falling, swimming through the air, etc. Nolan also addresses the personal aspect of dreams as Cobb's haunting past threatens to invade his subconscious as his team steals the most intimate secrets from their targets.
For all the necessary exposition, it doesn't become tiring or disorienting. Things are well-explained so that it never feels like your being drug along without all the pieces, but it's not overly pedantic. I found that I was able to predict certain major plot points in the film, but my ease of predicting certain points distracted me from searching for too many answers so that each scene held more surprises. With the exception of the too-long, disorienting snow ambush dream sequence the film is well-paced and attention-holding.
The thing about Chris Nolan is that he thinks big. Like the flipping semi in The Dark Knight, visually striking moments are best achieved through being willing to take risks and think one step simpler than the immediate reliance on CGI. Joseph Gordon-Levitt gets the chance to star in an extended sequence that borders on impossible yet looks almost flawless.
As usual, Nolan does not leave the film on the screen when the credits roll. This film asks to be pondered, but without answers. Unlike Nolan's earlier film, The Prestige, the joy of re-watching this film is not seeing how each scene reveals pieces of the whole mystery, but rather in choosing fresh what to think about the story with each viewing. As noted by these guys, Nolan's developing career is revealing an obsession with obsession, and I think nothing fits this better than a film that fails to offer solid resolution.
The cast is brilliant. Yes, I think that Leonardo DiCaprio is one of, if not the best actor of his generation, but the rest of the cast is so exceptional that he doesn't even steal focus. Ellen Page's performance isn't striking, but it's clean and earnest. Gordon-Levitt continues to pick excellent films and transform with each of them, and Tom Hardy is really excellent. In addition to it's filmic and stylistic merits, Inception is also entertaining. There are flawed moments in the film, but there is also a great balance of mystery, action, tension, and comic relief.