Measure for Measure
This Shakespearean play is considered either a comedy or a "problem play" by well learned authorities, upon finishing this play I side with the latter. There are three main arcs throughout the play: the Duke disguising himself to view his dominion with another perspective, the upright Angelo using his authority for dishonorable behavior, and Lucio. Overall the first two arc intertwined pretty well, though I can't remember if Angelo and the disguised Duke had an interaction before Act V but I think it didn't; if an interaction had taken place it would have made Act V that much better. Lucio could be argued as being a comedic element, but he was just an annoyance throughout most of the play especially Act V.
Given how the play finishes, it isn't a comedy. Because Claudio doesn't die (though others supposedly do/will at play's end), it can't be a tragedy. Thus the label "problem play", maybe in the end it was just a morality play and nothing more or less.