“By far, the wittiest and most cinematically literate movie ever made to market a plastic toy, writer-director Greta Gerwig’s box office juggernaut “Barbie” is a surprise feast for movie buffs, crammed with so many allusions and homages to classic films that we critics could spend the entire running time Ken-splaining all the references. A more enjoyable alternative can be found at the Brattle Theatre this week, where the ingeniously titled retrospective, “Barbie’s Roots,” takes us through some of Gerwig’s artsier and more unexpected inspirations for her billion-dollar blockbuster.” – Sean Burns, WBUR