Everyone rightfully points out Cagney's bravura performance, but Curtiz's direction is nearly flawless. Say what you want about Curtiz's auteurist credentials, but his direction in this film as is about as good as anything I've seen in the great decade of 1940s cinema.
Heavy on histrionics, not to mention factually inaccurate, but damned if it isn't highly entertaining! For once the Oscars got it right by (finally) awarding Cagney for one of his finest performances! His turn as George Cohan is full of emotion and gravitas as well as being on the money physically.