I was one of the few who actually saw the original B'way production of Merrily We Roll Along. By the end of the show I was a sobbing mess. I once heard the show described as a comedy, but in my eyes it's a tragedy. Missed opportunities, shattered dreams...and a score full of wit and heartbreak.
OK.
However, I was responding to the poster that called Sondheim his favorite living composer, assuming he meant composer of musicals. Alas, Gershwin stopped qualifying for that honor some time ago.