I think I said before once or twice that a good "plot twist" should:
1.) Not be totally predictable
2.) Should explain/detail events that happen before the twist.
Or in other words, they shouldn't just be totally targetless curveballs for the sake of a 'twist'. You want to catch people by surprise, but it should make sense regarding the narrative as a whole, especially how the twist was approached.
I felt the GitS 'twist" yesterday, while not a series changing event, fit these pretty well. As the conversation between LM and Serano continued, I was getting a little confused why it was going into so much detail about their prior meeting and other useful pieces of information. It was starting to feel too convenient for the viewers for a moment, and almost seemed like lazy storytelling (here's a buch of helpful information that we are for some reason discussing now!) . But as soon as the ending of the episode rolled around, the reasoning behind 'LM's' actions and the whole episode make a lot more sense.
Well done.
Well, this episode could have gone one of three ways.
1. The way it did. Major had the information from the Laughing Man, but she needed Serano's testimony to get anything done against the powers that be.
2. It could have been her monologuing the laughing man info dump to the chief or someone and then have them snatch Serrano up later.
3. She could have kept it all to herself and brought it out later at the end of the case and they decided just to pursue Serrano as he's the only one alive with the info they need.
The show tries to fool you into thinking it's going to be 3 but if you look VERY CLOSELY the Laughing Man's eyes are not quite the same as they were previously. It helps that they have the same hair color.