½ Iron Man 3 The weakest in the series, it suffers from confused plotting, flat-footed exposition, and more pure, noisy nonsense than even a comic-book movie should have to put up with. Yet whenever Robert Downey Jr. cuts through the claptrap, it’s still the most subversive Marvel franchise around. With Gwyneth Paltrow, Guy Pearce, and Ben Kingsley. In 3-D. (130 min., PG-13) (Ty Burr) Full story for BostonGlobe.com subscribers.