Cymbeline is not, to put it charitably, one of Shakespeare's finest plays. The language, while sometimes rich, is often clumsy, and the mediocrity of certain scenes (notably that witnessing the bizarre appearance of Jupiter in V.iv), have led a number of critics to suggest that the Bard collaborated with a less talented playwright in writing this play. The work does feature a number of excellent characters, including the wonderful and almost perfect Imogen and the entertaining Iachimo, but the title character, Cymbeline himself, is never developed or analyzed, and most of the supporting cast lacks depth. Imogen's husband, Posthumus, has an unfinished air about him; his character is at once difficult to make sense of and utterly unlikable, and he is manifestly unworthy of his wonderful bride. Structurally, the various scattered subplots effect incoherency, and they only find integration in the final scene, while major characters disappear from the action for extended periods of time--notably Posthumus, although his absence from the middle of the play may be considered a blessing.
Cymbeline often feels like a deliberate pastiche, in which the aging Shakespeare revisits various elements of his earlier plays, albeit in a less impressive form. The Cymbeline-Imogen relationship invokes Lear and Cordelia in King Lear, but while Imogen may be Cordelia's equal, Cymbeline is a nonentity. Iachimo's deceptions (not to mention his name) call to mind Iago's machinations in Othello, but this scoundrel, while zestful, hardly achieves Iago's level of villainy. Similarly, the petty Posthumus is never more than a mere parody of the raging Othello. The sleeping potion evokes Romeo and Juliet, and Imogen's cross-dressing recalls the great comedies, but these various elements never coalesce into a thematic whole, and the play suffers by comparison with the great works it echoes.
Nevertheless, Cymbeline offers its share of delights. Imogen is a worthy creation, and she has been a favorite of male critics for centuries, who have often presented her as a kind of ideal woman. Iachimo, while hardly deep, is a fun villain to watch--clever, well spoken, and not truly evil enough to hate. And the play is entertaining, if nothing else: It is filled with plot (in fact, it is all plot), confused as this plot may be, and provides us with swordfights, disguises, poisons, and two eminently hissable villains in the Queen and Cloten. Indeed, the entire story contains many elements of the fairy tale--including the best element, the happy ending.
The finest scene, in such a work, is inevitably the final scene, in which all the tangled strands of plot unravel in a brilliantly constructed series of revelations, and everyone receives their just reward. The villains die, Imogen and Posthumus are reunited, and King Cymbeline's abducted sons are restored to him. Indeed, while the play invokes famous tragedies, these invocations heighten the relief at what doesn't happen. The king errs in his marriage and his treatment of Rome, but his kingdom survives; Imogen and Posthumus both mistakenly believe the other to be dead, but they do not kill themselves out of deluded grief; Cymbeline loses his sons but gets them back; the Romans are defeated but their lives are spared. Tragedy looms but never strikes, and, instead, as Cymbeline declares, "Pardon's the word to all" (V.v.422).