Very brief review, because it doesn't deserve much more. Good points: very expensive CG and special effects budget, maybe 10% of it intelligently spent. Some effects were stolen wholesale from The Matrix, one of the effects was stolen from an old Fred Astaire movie. Another was straight out of an Escher drawing. So many things exploded I had to double-check imdb to see that Quentin Tarantino wasn't involved in the production.
At 2 hours and 28 minutes long, I was checking my watch after an hour.
A short break for the good stuff: the obligatory Sweet Young Thing genius is a clone of Summer Glau, except without the martial arts/stunts ability. There were moments of reality-bending which were very effective. Ken Watanabe's final scene, if that was indeed Ken Watanabe (I have my doubts - the face looked too Caucasian) showed some acting chops. It's science fiction - I would not be surprised if the idea came from Ursula Le Guin's Lathe of Heaven. At its core it is based on the same "what if?".
Casting was absurd. None of the actors were believable in their roles, except Ken Watanabe and that's because he was a total racist stereotype. And THE SOUNDTRACK. Oppressive, uninspired, way too loud throughout. Most of the film, and all the thousands of action sequences were made to look like they were shot with hand-held cameras. The motion mostly seemed artificial to me, as if they CG'ed the effect. Or had the videographer shake the tripod. It made me dizzy, and the sequences were all way too long to make their points. I spent a goodly amount of time listening to gunshots, machine gun fire and explosions with my eyes closed. For a movie about dreams, it was far too violent.
The ending is telegraphed early and often, the final 10 seconds gives us the confirmation but most of us saw it coming hours before.
Finally, I liked the idea of the freight train, but it would have worked better with a sharper image. I watch HDTV for a living - I'm spoiled.