Back when Jim and I took a Shakespeare class together, I chose not to review each play, or even the plays as a set because, for the most part, they didn't take very long to read. Plus, I just didn't read a lot of them. Shakespeare hasn't changed, but I have--King Lear is one of Shakespeare's most challenging works, and when I teach it in class I would like to know what I am talking about (or be able to fake it convincingly). So with this one I took my time.
That Shakespeare is better experienced with great patience and caution, savoring his wit and multiple layers of meaning, will come as a surprise to no one. Whether I enjoyed the experience more I cannot say. It's been years since I've read any of the other plays and, more importantly, King Lear isn't really a work meant to be enjoyed. It is inconceivably bleak--so bleak, in fact, that until the twentieth century, most of the time if you saw it performed you would see a version doctored by a scholar named Nahum Tate, which went so far as to add extra characters and replace Shakespeare's unhappy ending with a more palatable one.
Shakespeare's Lear is taken from the mythological Leir, a king of ancient Britain long before Roman conquest, and the story begins essentially the same: Lear, deciding to retire, wishes to split his kingdom among his three daughters, Goneril, Regan, and Cordelia, and says that he will give the largest portion to whoever professes that they love him the best. He expects that his favorite, Cordelia, will win this prize, but her humility and honesty prevent her from giving the same kind of empty, fawning answer as her sisters, and she is cut out of the inheritance and leaves to marry the King of France. Afterward, powerless Lear is mistreated by Goneril and Regan and their husbands, the Dukes of Albany and Cornwall, who strip from him his retinue of attendants and insult him until he is essentially driven out of both of their homes.
There is a subplot with another nobleman, Gloucester, and his sons Edmund and Edgar. Edmund, who is illegitimate and cannot inherit anything of Gloucester's, fakes a letter from Edgar professing to plan their father's murder, and Edgar must escape and take the disguise of an escaped lunatic. Eventually, the whole thing comes to a head when Cordelia and the King of France invade Britain to retake it from the forces of Goneril, Regan, Albany, Cornwall, and Edmund.
But Tate isn't the only revisionist. The Leir story, as recounted in Geoffrey Monmouth's Historia Regum Britanniae, ends with Cordelia victorious, and she goes on to rule Britain after Leir's death. But Shakespeare pulls a reverse-Tarantino and ends Lear for the worst, with Cordelia captured and eventually executed, Lear having long been driven mad by his indignation and shame. At the end, only Edgar, Albany, and Lear's loyal servant Kent are left alive.
Why did Shakespeare change the ending of the Leir story? I think this is the most interesting question that Lear presents. One reason may be political, as the events of the play reflect somewhat the reign of James I, who had attempted to do the reverse of Lear's actions and unite England, Scotland, and Wales, though it is unclear to me whether Lear supports or condemns James' efforts.
Another answer I think can be found in one of the play's most significant themes, the significance of nature. Lear is full of disguises, trickery, and false speech, and the "truth" is always clearer to the audience than it is to the characters of the play. In one great scene, Lear, Edgar, and Lear's fool have taken shelter from a storm in an old house, and they babble and talk circuitously--a man becoming mad, a sane man pretending to be mad, and a court jester, whose riddles belie the most wisdom of anyone in the play. These men appear to be quite similar, but in truth their natures are wholly different from one another. In another way, Lear's absurd wish that Cordelia appear to love him more than Goneril or Regan is what sets the entire tragedy in motion.
The purpose of the bleak ending, then, may be that Shakespeare is telling us something about life. At one point the half-mad Lear says to Edgar, "Nature's above art in that respect," i.e., the respect of suffering--more suffering occurs in life than can be truly captured in art. If this is the case, Shakespeare may be asking us to view King Lear, at its heart cruel, unforgiving, and senseless, as a mimetic work, imitating the cruelty of an unforgiving and senseless world.