Base-Breaking Character: Farrah Mahmoud, the hospital psychiatrist. On the one hand, many see her as a Designated Villain for Kate. Other times, she's an idiot who constantly gets her own diagnoses wrong, leaving Kate to clean up the mess.
The Scrappy: Delilah, Will's one-time affair-cum-stalker. Will has an affair with the waitress Delilah, and she becomes Yandere for him. But can't fire her from his business, as it would look like he's firing her for romantic involvement. After this is brought up, she mainly just exists to cause a minor inconvenience to Will and Kate before, and is eventually fired regardless. Ironically, in a similar situation to Joanne Froggatt post-Robin Hood, her actress had more success after the show was canceled.
Alternate Character Interpretation: Is Thomas dead at the end of the movie? Nolan seems to have full control at the end, and the last we see of Thomas is him stepping onto the void, implying he has ceased existing. However, given that he is basically a digital copy of the original Thomas, whether he is dead, shut down, or is still alive in some form within Nolan's mind has yet to be clarified. Making it even muddier is Dr. Brooks seeing him in the headset at the end.
He Really Can Act: Mamoudou Athie's acting as both Nolan, Amnesiac!Nolan and Thomas in Nolan's body is praised by fans and critics alike.
Phylicia Rashad is no slack either, playing both a doting doctor and a Mad Scientist playing God.