Mank shows that David Fincher can make something that's nothing like the rest of his filmography, not bound to his own rules and conventions. It may not be entirely accurate in its depiction of how Citizen Kane was written but it's fascinating to see Fincher of all people go against auteur theory.
Gary Oldman is amazing. He's witty, self obsessed and unable to back down regardless of the consequences. His relationship with Amanda Seyfried is great, especially a walk around the gardens in which she shows she's so much more insightful than her peers give her credit for.
David Fincher's direction is a lot stronger in its visual and audio composition than its narrative construction. Going back to old Hollywood he crafts a film that truly belongs there, the black and white cinematography and the overall audio really feel of the time. However, the flashback heavy structure of the film robs it of what little momentum it has.
Trent Reznor and Atticus Ross also change things up from their usual output, displaying a completely new set of skills. Their score is fantastic, feeling era appropriate in the same way everything else does and it's definitely some of their least subtle work.