Is anyone else convinced that this MUST have been a collaboration? It's head and shoulders above anything else he's done
Macbeth is sub-par compared to most of his other works and only studied at a highschool level because it shows how aspirations can evolve into self destructive obsessions. But sure, let's go with "head and shoulders above anything he's ever written".
The only part of the play that might not have been written by him is the song of the witches in act four scene one. Although at the moment I can't remember who was theorized to be the other possible author.