Voter said: "I feel like I remember an identical thread about a year ago?"
There was. I remember saying that I would have wanted to go back to see the opening night performance f Bells Are Ringing (even though I knew from the movie and cast album that I would be bored for some of the (dated) numbers). I loved Judy Holliday in everything I saw her in and would have loved to see her live, especially in a show where her character had nothing but great songs, including one of the all-time great 11:00 o'clock numbers.
It's always an interesting topic.
I most enjoyed Merle57's post, since I saw virtually every show that Merle57 mentioned, plus two that were either left out intentionally or forgotten: Fiddler on the Roof, which I think opened in Fall 1964 and would remain open for another 8 years, and (possibly) Half a Sixpence (not sure when it closed)...it opened in the same season as Fiddler and ran about 15 months, so it could have been closed. Also, in those days, Lincoln Center staged 2 musical revivals at the (then) New York State Theatre, and the second musical after Annie Get Your Gun was a production of Show Boat, with outstanding performances by Barbara Cook as Magnolia, Constance Towers as Julie, and William Warfield singing Old Man River.
Thinking back to my 16 year old self, you really were right. There were an incredible number of great musicals open at that time. So many classics in their initial production. The only things that you might have regretted wishing for if you were able to see them were A Time for Singing, which was all about the male chorus and was really boring; and Skyscraper, which was just mediocre in every way. It is criminal that Julie Harris received a Tony nomination instead of Joan Diener; in her first and only musical, even at 16, I could see that she had no stage presence in a musical. While On a Clear Day was not a great show, it was thoroughly enjoyable and was my introduction to Barbara Harris, whose greatness as a musical comedy performer was sadly exceeded by her success in avoiding Broadway after The Apple Tree.
But to think that the original productions of so many shows that became true classics were all open at the same time is pretty amazing when I think about it.