Spoilers: This post has them.
Inception is a cool movie, visually speaking. But beyond that, I don't think it has much. Leonardo DiCaprio's character is the only one who is developed, but all we get is that he loves/loved his wife and loves his children. The character of the mark (the son of the dying business man) is developed a little, he seeks his father's acceptance (this is pretty thin, though).
A lot of the material I've seen online says how amazing this film is. I agree it is visually amazing. But that's not what people are talking about, it's the question of what was real and what was a dream and whose dream it was.
And all of that is irrelevant.
Does it matter if the ending scene is a dream or not? No. It doesn't. Not one bit. Because these aren't real people, and we don't learn anything about anyone from it being a dream and wondering whose dream it may be. Does it matter which scene belonged to which dreamer, and were there clues that we had been mislead? Irrelevant. That may be fun, but it doesn't tell us anything. Is it revealing about the characters? No, because it needs to be revealed more clearly, and even if it is, so what? They're characters in a movie, they're not real, there is no insight here except about what the writer, director, and producers wanted to do in the film.
Does it matter if Leonardo DiCaprio's character has been in a dream the whole time? (I think we see the spinning top work at some point, but I don't exactly recall.) No, it doesn't. It's a movie, it's not real, it itself is like a dream. There is no reality in it. If LDC's character is in a dream at the end, then he's in his dreamworld fiction inside a movie fiction, so it's fiction. If he's not in a dream at the end, then he's in the movie's real world inside a movie fiction, so it's fiction. It does not matter. There is no weighty intellectual discussion here, unless you're in college and you think you're much smarter than you actually are (and then it is neither weighty nor intellectual, but sadly it is a discussion).
It's not even as if dream and unreality sequences are new to science fiction movies, we've seen it with the Matrix, but we've seen it before with stories such as The Wizard of Oz and Alice in Wonderland. The Wizard of Oz is old, it was written in 1900. That doesn't mean it isn't an enthralling idea 110 years later, but we've seen it before.
Visually Inception is a great, fun, inventive, beautiful movie. Beyond that, it's pretty standard. There's nothing wrong with that, but all of these people and critics think there is something weighty about the dreams. There isn't.