As a film, Michael Jackson's This Is It is fairly straightforward, a series of musical numbers shot during rehearsals for the spectacular 50-show concert Jackson planned to stage at London's O2 arena but didn't live long enough to perform. As a cultural artifact, though, it's something more compelling: the final act of a pop legend, all the more powerful if you were one of the kids who bought ABC on a 45, danced your way through high school to the beat of Off the Wall, huddled around a TV in your college dorm to watch the MTV premiere of Thriller and wondered in later years: ``What happened to his face?''