What Are Shakespeare's "Problem Plays"�?

This name is usually given to three plays written around the time of the death of Elizabeth 1. They are "Troilus and Cressida" (1602)," All's Well That Ends Well" (1602) and "Measure for Measure" (1604).
These are regarded as problem plays mainly because they are difficult to classify. The last two in particular are essentially comedies, but their mood is dark and cynical, and it's very questionable whether their endings can be regarded as the happy ones expected in a comedy.
Briefly, "Troilus" is a story of infidelity and betrayal; in "All's Well", a snobbish nobleman is tricked into marrying a woman he despises; and in "Measure" a Puritanical governer condemns a young man to death for having sex before marriage – and then offers to pardon him in exchange for his sister's favours.
These plays are fascinating and controversial, but certainly not straightforward, which makes the description "problem plays" highly appropriate.