At the very beginning of Happy Death Day, while the Universal logo is appearing, they did something clever. It hitches like a record scratch and restarts, twice, before proceeding. Just enough to let you know what you’re getting into, right?
Happy Death Day 2U starts with a mild similarity, in which the hitch splits the screen in two, and then in three. Which, if you don’t know what they’re going for, I guess it would be a spoiler to tell you? But anyway, my point here is mostly to say that I believe the science fiction slasher movie is wholly untrodden ground, and they deserve props for this alone.
Except for the slight genre shift, though, the movie follows an extremely important rule of horror movie sequels, first spoken by Joe Bob Briggs more than thirty years ago, and here I am paraphrasing: Just make the same damn movie as you did the first time. (In some ways this movie takes the advice even more literally than is typical, but that stands to reason.) But yeah. Starts on the same day the last movie ended? Yes indeed. Follows (mostly) the same characters who are faced with (essentially) the same problems? Aye. Rule: followed!
The plot is so full of holes that it would more properly be referred to as a colander, but neither movie takes itself very seriously, so that’s fine. Plus, the more serious parts are actually thoughtful and touching, which gives them even more leeway as far as I’m concerned. As long as they keep the same cast and (I presume) writers/directors, I will cheerfully watch (and probably rewatch) these movies in perpetuity.
 Citation needed.
 Haha, beat you to it. It’s possible I could find it, if he was writing for the Dallas paper that still exists and if they have internetted their 1980s archives. I first read it in a book of collected columns, so.