There are no structure problems at all in the screenplay. None. I can agree with you that perhaps a couple little lines of dialogue were not perfect, but that's ultimately irrelevant. What you perceive as "exposition" or "explaining the rules of Inception" is only a very surface level reading of what is happening in the film. That exposition is not a plot device but rather inherent to the fabric OF the plot. It is a continual entrenchment into the human mind and an exploration of how thought itself works.
Furthermore, going by one of the many interpretations of the film that simultaneously exist at the same time (the film essentially acts as multiple universes at the exact same time), the "exposition" is in fact the reflection of Cobb's therapy (the DiCaprio character) and his quest towards catharsis. The Ellen Page character is continually asking questions and pushing against the boundaries of his perception because Cobb is in fact the subject of inception throughout the film. The only way for him to get over the death of his wife, a pain that has taken over the core and essence of his entire being, is for a team to incept the idea into his mind. And since Cobb himself is the most talented individual in the World at such things, the only way to incept HIM is to create a scenario where he believes he is incepting someone else. Thus, the plot of the film. If you scoff at this potential interpretation, just look at how dream-like his perceived World is. The way he is able to squeeze through a crack while being chased. The way helped suddenly arrives to rescue him. Many other examples I won't delve into right now.
But that's only one interpretation. There about half a dozen possible interpretations of the film and the beautiful thing is that they all work, sometimes at the same time. The film thus becomes a touchstone to dreaming and memory and existence itself, showing how unquantifiable those properties are. Or, rather (in addition), it becomes a touchstone to circular thinking - just like the Escher staircase that is depicted and used within the film. But it's not just philosophical musing either because, again, the film's core is wrapped around an incredibly emotional and immediate depicting of human struggle and the vast wasteland of emotion within all of us that we have to overcome to defeat our demons. It's simply one of the best films ever. Period. (I completely disagree with your criticism of the cast as well, especially the bizairrely AGEIST criticism you are leveling against the film...it was the best Ensemble of the whole year with no weak performances at all, some wonderfully subtle moments from DiCaprio amongst the anguish, one of Marion Cotillard's best and most haunting turns ever, and a pitch-perfect and unique characterization from Tom Hardy)
Mistakenly, the film received tons of praise for being "visually/stylistically amazing" but received criticism for lacking substance (or being "too confusing" ). No, No, NO! Exactly the opposite. The film could have been quite a bit better in terms of the visual shaping. I mean, it's still rather creative in that regard, but not in as dizzying of fashion as it might have been. The overlapping temporality and such certainly already makes your mind spin a bit (a phenomenal accomplishment in Editing this film most definitely is), but in terms of cinematography and the entire usage of space in every single frame and the creativity of the images, I do agree with people saying more could have been accomplished. The film is still an overwhelming masterpiece, though, because of how complex and effective the ideas and narrative thrust and humanistic draw is. But it's so frustrating how the "high brow" audience won't accept the film because it isn't visually esoteric enough and how the "middle brow" audience won't accept the film because the amazingly complex and powerful emotions and ideas here are not spoon-fed to them.
Oh well. A lot of Hitchcock's best films weren't well received at first either.