This year’s offerings at the Humana Festival of new plays followed some common themes. “Bad endings in America? Mopey zeitgeist? Metaphorical navel-gazing? Armchair quarterbacking the philosophical arc of the Humana is the second-most-favorite pastime of the festival. (Relentless schmoozing is, of course, numero uno.) And because so many of this year’s scripts seemed not-quite-fully realized, there was plenty of room for interpretation.”