LogFAQs > #978804201

I'm not an expert in this field, so I might be off base/exaggerating, but since no one else is arguing for it, I feel I should point out that Show Boat is regarded as the first "book" musical. I'm sure it wasn't the actual first, but it's responsible for moving musicals away from the revue style and into plays with actual plots.

Also, since no one's mentioned it so far, and while I don't think it deserves to be on the list, since it lives in the shadow of The Lion King I want to give an honorable mention to Beauty and the Beast. It was very influential in its own way albeit not for reasons directly related to theater itself. Disney bringing it to Broadway was widely blamed/credited (depends who you ask), with causing the city to double down on cleaning up Times Square so whenever someone speaks of a location being "Disneyfied" this is the genesis of that term.