The plot is actually very complex, but it's easy to understand if you pay enough attention. Like I know pretty much the whole story in my head, it's just hard to explain.

There are still some things that confuse me, but I pretty much got it.
When I first got in my seat and started watching the first few scenes, I was like "Crap, this is another one of those movies where you have no idea what's going on." But as the story unraveled and Ellen Page's character became introduced, you really start to get the feel of the story.
Ellen Page and Leo DiCaprio also worked great as a team. They had really good chemistry in the movie and honestly, I could hardly recognize Ellen, as she was not playing a sarcastic teen (Juno). But the whole cast was amazing, each one delivering their own great performance.
And as for the cliffhanger ending, I was kinda mad, but I figured it would end somewhat that way, always wondering if you're living real life. But anyway, the movie was really complex, but creative and clever at the same time. It was one of the best movies I've seen in a while and it's all I've been thinking about since I got home from the movies a few hours ago.