Ewan mentioned, while filming The Island, I think, something about working with people and sets and how difficult it is to work against green sets. It was reported as he disliked working on the prequels. Gah. I'm sure it WAS difficult working against a green set rather than against fellow actors. It may not have been the best working situation. It does not mean he disliked working on the prequels (which tends to imply something against the script, or GL, or his fellow actors...); it just was difficult. Dark Obi? Play on his guilt? Take the Force away from him? Weaken him while simultaneously showing him how he can't do anything to anything to help others and force his grief/guilt into anger?