What does Veronica Roth do that makes it so interesting?

    So, I'm reading Allegiant and just like Divergent and Insurgent, I'm completely hooked. I'll try not to reveal any super special secrets or anything. But, in most series, the author comes up with a brilliant idea in the first book and then the last two books aren't quite as great. When it comes to the Divergent series, that tradition doesn't apply with Veronica Roth. There's also another tradition about stories that just get old, and your readers get tired of hearing these stories. Once again, Roth somehow finds a way to break down these barriers.
    My theory is that she has many different stories within the same main idea of the series, Tris, a teenage girl is put in several situations that decide the outcome of her life. That's pretty general, I see. But, each of these different stories are so developed, and transitioned so well that it sounds like a complete masterpiece. But, then Roth adds in plot twists and cliff hangers that take the story to that next level and to a complete masterpiece. All this completely and totally compels me to read more!