I loved Season one of Code Geass and consider that one of the best that anime has to offer.
I also loved Season two. Why would I give an anime that I love only a 6?
The problem is that the character's motivations become shallower and shallower to create that same chessboard concept that occurred in season one.
In the first season it all felt natural. Each character felt like they did what they did was their choice.
In the second season it felt a little more forced in that this character has to do an action in order to keep the story moving. The plotline is genius but it comes at the cost of authentic character motivations.