I watched Shutter Island, The Machinist and Oldboy because of this here thread!
Shutter Island's twist was so obvious that I thought it couldn't possibly be the twist and that it was a double bluff. Nope. Still, the moment at the end
(SPOILER)was more of an Inception "Was it or wasn't it?" with his little comment about being a monster rather than a twist imho. The sets/direction were sweet though.
They were pretty sweet on The Machinist too. I sort of got the twist on that one.
(SPOILER)It was obvious that Ivan was Trent Reznor but I couldn't quite get what the hell he'd actually done. It was a little vague on that.
Oldboy was a smurfing amazing film, my favourite of the three. I had the thought of
(SPOILER)"Could this woman be his daughter...?" but later abandoned it when they banged. WRONG!