This is a really good question.
In style/structure: Oklahoma!, Hair, A Little Night Music (the complexity of those lyrics, wow - I love how lyricists attempt to follow Sondheim's patterns, e.g., Fun Home, which Lisa did wonderfully), Beauty and the Beast (THE Disney musical - inspired so many others).
Social impact: Wicked ($$), RENT (I love that Lin quote @A Director posted), In the Heights (that diverse cast and Lin's rapping - I loved it), Les Mis, The Phantom of the Opera ($$), Grease, Hamilton (the diverse cast, but I can't see it necessarily impacting Broadway in terms of style; I thought that would happen with "In the Heights" and it never did; but Hamilton might? I don't remember a show receiving this much buzz in a while.).
I know I'm forgetting many, but these are the my top ones so far.
Every so often there was a rare moment of perfect balance when I soared above him.
Updated On: 8/20/15 at 12:20 AM