Of late, filmmaker Robert Zemeckis is a somewhat confounding figure. The director of such beloved films as the “Back to the Future” series, “Forrest Gump,” “Cast Away,” “Death Becomes Her” and “Who Framed Roger Rabbit” has delivered almost as many duds as hits, if you also take in “The Polar Express,” “Beowulf,” “Welcome to Marwen” and “Pinocchio.” An experimentalist obsessed with special effects and the dramatic power they can exert in cinema, Zemeckis is always trying something new, especially with motion-capture technology. It doesn’t always work, many of these projects drifting into an unappealing uncanny valley. Despite his experiments, he hasn’t quite nailed it yet.