"Concept" musicals can have a bit of a tough go of it. Musical theatre audiences (more so than non-musical theatre audiences) are generally looking for the formulaic from their evening's entertainment. Subject matter or setting may not be important, but they're looking for certain things to happen in the first act and certain things to happen in the second act.
The late 80's musical Romance/Romance (Off-off Broadway in 1987 with a move to Broadway in 1988) turned that notion on its ear by telling two distinctly different tales (different settings, characters, etc.) from the first act to the second. The roles were played by the same actors, but - other than that - the only links between the two stories were the theme of romance and one musical number.
Romance/Romance achieved reasonable commercial success and considerable critical success including Tony nominations for Best Musical, and for Best Actor and Actress, respectively, for Scott Bakula and Alison Fraser in the leads.
Here they are performing numbers from both acts (with a swift costume change) on the 1988 Tony Awards. (This was not long before Bakula would land the career-making role of Dr. Samuel Beckett on the acclaimed sci-fi series Quantum Leap.)