Put me in front of a biopic and watch me squirm with frustration. Real life is fascinating but rarely makes for a finely judged story. So I came to “On the Basis of Sex” with apprehension (especially as I’d missed seeing the much-lauded documentary “RGB” about Ruth Bader Ginsburg). I shouldn’t have fussed: Mimi Leder is an excellent director, with an intelligent, finely balanced grasp of story and drama, and the script from Daniel Stiepleman barely puts a foot wrong. Perhaps the reason that this biopic works is that it isn’t really a biopic. Instead it sets the scene with some early-life flashbacks and then settles into a tense, inspiring look at Ginsburg’s very first success at changing U.S. legislation on the basis of sex discrimination. And what a drama it is, with the outcome swinging on a few minutes’ testimony by feisty, whip-smart Ginsburg. Felicity Jones produces a career-best performance as Ginsburg, and Armie Hammer ends up delivering the goods as Martin Ginsburg even if he looks too wholesome. The chauvinistic villains are played by capable character actors. I was swept up by the rousing tale, one little told, and didn’t come down until the abrupt but smart ending. Recommended.