The documentary filmmaker Frederick Wiseman, now 90 and still working, employs a fly-on-the-wall approach that is deceptively simple yet yields fascinating results. In City Hall, his latest film, Wiseman observes and records the day-to-day operations in Boston’s City Hall, where the city’s Democratic mayor, Marty Walsh, presides. Wiseman’s camera tracks Walsh’s juggling of daily tasks and long-term projects, his unswaying egalitarian beliefs. It sits in on complex political debates. Run time is 272 minutes, and those four and a half hours shed light on just how complex it is to govern a city—even one that’s small and well organized. —E.C.