I love Sunset Boulevard too. I just watched the Bogdanovich Buster Keaton documentary and had forgotten Keaton had a cameo in Sunset Boulevard! That documentary just reminded me all over again how quickly the advent of sound changed everything (I had no idea Keaton was in so many talkies); it's a big reason I love Singin' in the Rain too. (I mean, the biggest reason being that threesome oh my god.)