No spoilers, just a review.
Good concept, good story, good movie, but it's not great. I definitely wouldn't rate it above anything else Nolan's done so far. I'm a bit disappointed since I heard he dwelled on the story for like ten years before writing it. I was expecting it to be his masterpiece, but I wouldn't give it more than 4/5 stars, with 3.5 probably a closer rating.
Compared to how dreams were portrayed in Eternal Sunshine of the Spotless Mind, Nolan portrays dreams as rather sterile. Perhaps he thought the car chases and gunfights would make up for the dream world being a reflection of the real; or perhaps he wanted to mirror what I presume is everyone's dream-reality (ie the vast majority of my dreams, or the ones I remember, occur in normal settings). But while I can understand and rationalize on his behalf, I still would have preferred to see the dream settings exaggerated. Aside from watching the city fold over on itself, the most interesting visual effect is when Joseph Gordon Levitt (JGL) has a zero-gravity fistfight in a dream hotel. If Nolan had incorporated some Eternal Sunshine-like visual elements/motifs, I think the movie really would have taken off. As it is, in terms of execution it kinda just glides.
And another strange thing happened for me--I found myself more interested in JGL's character/performance than Dicaprio's. Yeah, Dicaprio's character was the center of everything and had all the secrets, but some of his performances (perhaps an extension of the writing) were overly dramatic, whereas JGL's character was more believable, and for me, somehow more likable. But I'm glad it was cast the way it was, because I can't imagine JGL in the lead role. I think it might have simply been that he was perfect for the role, or as much as I hate to praise people for pretending, maybe he's just that good of an actor.
The bottom line is it's worth seeing, but not necessarily in the theater. Now that I've seen it I realize I could have waited for the Blu-Ray.