... first reading (or watching an adaptation of) Agatha Christie's The Mirror Crack'd From Side To Side. Not that it's her greatest work, but without going into spoilers, this outright plagiarizes from that book.

This is part of why it's so bad, but Knives Out, though predictable, was still fun and had some sense of internal logic. Glass Onion loses the fun and its humor consistently fizzles flat; in the last twenty minutes or so, every character (still alive, anyway) makes at least one very dumb decision.

Craig still brings some fun to the role, but Benoit Blanc is consistently portrayed as the absolute stupidest "world's greatest detective" that has ever been. In this one, he's sort of like Indiana Jones in Raiders; he really has no effect on the plot and isn't smart enough to figure very obvious things out.

If you want to watch a great murder mystery film, check out the 1965 Ten Little Indians adaptation, the 1974 Murder On the Orient Express adaptation, or the 1957 Witness for the Prosecution. If you want to watch a good murder mystery film, check out The Last of Sheila, Evil Under the Sun, or the 1940s And Then There Were None. If you want to watch a truly terrible murder mystery, it's Glass Onion or the Frank Stallone And Then There Were None.