I'll echo the recollection of the other old-timers who saw the first run like I did (and you know who you are ) Definetly the bloody horse head - big yech noise in the audience and then the Sonny Swiss Cheese scene.

But as far as other buzz, I think the Brando casting as Vito received the large share of press chatter. Was he washed up? Was he the right type? Wouldn't Anthony Quinn have been better. Lots of doubt. Look how it turned out.