See, I felt like the exposition didn't start until about twenty minutes into the film. It opens with Saito and Cobb's shared dream without explaining the logic of shared dreaming at all until later on in the film. It may not have been as confusing as Memento but I wouldn't say it's straightforward, at least until you've seen the film once. Of course, if you went in already understanding the film's mechanics of shared dreaming and had a bit more background on what the film was about, it would probably be easier to understand, but I went in having seen nothing but the trailer.
Maybe it wasn't the first twenty or thirty minutes that were confusing - I have a hard time keeping track of elapsed time in cinemas. But in the first several scenes I definitely got the impression that I didn't understand even half of what was going on. (Note: I have yet to see the film a second time, which I need to remedy).