While all of Allen's early comedies are pretty wonderful, this film represents a big leap in technical proficiency. For the first time you sense him really thinking about how the camera is telling the story. And in finding Diane Keaton, Allen was finally paired with an actress who's comedic strengths were a great match for his.
This film relies less on verbal jokes (although there are brilliant lines) and more on visual gags. It almost feels like you're watching a great silent comedy at times.
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Better music too, with jazz taking over from traditional score the first time in Allen's films.
A funny, inventive, sophisticated if sometimes wonderfully silly comedy, with almost no dead moments. For me it represents the beginning of the shift from Allen as a brilliantly funny writer and comic who happened to make films, to becoming one of our very best filmmakers.