IMO, why Kreia deliberately chose to use difficult words and ramble about the nature of the Sith and the Jedi alike, was just a way to point out her insanity and her character. And that made her interesting.
Her being evil from the start wasn't a plot-twist at all, atleast i never interpreted that it was supposed to be a shocker. The plot wasn't deep or complex either, it was simply a personal journey for the Exile, and that's were it succeeded with great use of skills in conversation, influence and so on.
Finally, The 'complex'-part is just buzzword created by the reviewers, unable to write something with actual content in order to satisfy the ADHD-generation of subcribers of their magazines.