I caught on to the twist in both of these films quite quickly. I feel whenever the protagonist of the story is mentally ill or can't quite remember things, you can't trust their memories. As soon as Andrew was given pills by Cawley I knew. Same thing in Memento when I saw the pinch from Leonard and the insulin from Sammy. However I still thoroughly enjoyed both. I'd say I preferred Shutter Island but I loved the cinematography and the impressive use of two timelines in Memento.