Nick Riley’s review published on Letterboxd:
Conceptually confused between a glossy concert documentary and a Behind the Music retrospective spoof, Popstar is all the good and bad of The Lonely Island stretched to the breaking point. If you like their brand of (rather obvious) farce and light commentary on vapid pop music culture, then this will be pleasant enough of a watch. If not, there's little witticism to supplement the largest parade of cameos since Anchorman 2 standing in for actual depth.
Also, Amy Schumer did the TMZ joke much, much better.