I just finished watching this series myself, and I was wondering what other people thought, throughout the entire series, is the most interesting and unexpected plot development. I'm talking about anything plot related.
For me, it's when Lelouch accidentally used his Geass on Yuffemia, when it went out of control for the first time. I thought it especially interesting, because he decided that he would work with her, and he was trying to explain how his Geass would have helped him out in any way, and accidentally uses on her to make her crazy and kill all the Japanese.
My only problem throughout the show also comes with this part. When he is later asked if he used his Geass on Yuffemia, he talks and acts as if he did it on purpose, but it is clear that he did not. For example, Suzaku asks him "Did you use your Geass on Yuffie?" and Lelouch just responds "Yes," Not "Yes, but it was an accident" or anything of the like, as if he planned it. That's the only thing that really annoys me.
So, what does everyone else think is the most interesting and unexpected plot development in the entire anime? I want to know!