“Unexpected Joy”, a new musical at the York Theatre Company, contains several unexpected joys: a groovy, folk rock score, an intriguing original story mining contemporary themes, and a quartet of strong female vocal performances; and some unfortunate faults: a script and direction lacking dynamism, stereotypical characters and sitcom-deep dialogue, and a pat ending.  The whole show feels dated and unrealistic, with an “agree to disagree” closing message about LGBT equality that I found troubling.