Here’s the eighth installment of the extraordinary long-game documentary with which filmmaker Michael Apted has checked in on a diverse group of British citizens every seven years since they were kids in 1964. We needn’t be scholars of a class-stratified former empire to enjoy it, merely alert to the ominous and soul-stirring privilege of beholding how quickly other people’s lives, and our own, fly by. Thus “a glimpse of Britain’s future” becomes a steady-gaze survey of its recent past, most notably the global recession, which seems to have affected…well, nearly everybody. It’s also a survey of evolving movie formats — from black-and-white to color, from grainy film stock to crisp digital video — and in spite of increased technical facility also increasingly a burden for its participants. At 49 Suzy said she’d stop, but here she is again, feeling loyal even though she hates it: “It’s like reading a bad book; I’ll still see it through.” And here’s Peter, who’d dropped out after some political complaints in 28 Up left him buried in hate mail, finally feeling better in his own skin (and wanting to promote his alt-rock band besides). Ever in flux, the others have gone on accumulating vocational or matrimonial failures, but also successes and fulfillments, like grandchildren. Apted keeps his material well organized, his questions frank, and his pacing brisk. In his hands, what might otherwise seem cruel — getting all these plans and dreams on the record, then returning over and over for an accountability review — counts instead toward a grand human affirmation.