How is Macbeth a good 21st-century play?
Macbeth remains relevant in the twenty-first century because its themes are timeless. Ambition, political corruption, and human folly are elements of the human condition which have yet to go away and more than likely never will. As others have mentioned, the basic story has been adapted by various different cultures, since these issues are universal too.
Also, the characterization is very sophisticated. Macbeth and Lady Macbeth feel real. They are psychologically complex, far deeper than one-note power-hungry tyrants in that they show guilt for their deeds. They do evil things but are not purely evil from the start. They are human.
As a story, Macbeth is paced well, atmospheric, and haunting. In the end, it's a classic tragedy—evergreen and never going out of style.
Macbeth, like almost all of Shakespeare's works, is timeless. The reason that the plays endure is because they deal with human foibles and triumphs that are common to all.
In the case of Macbeth, we see political betrayal, lovers with their own agendas, wives who regret acting in their husband's behalf, and punishment for unjust deeds. What's not to love??
Just in the last fifty years, Macbeth has been adapted to such unlikely locales as China and Japan, and has even been made into a musical.
I think so, primarily because of the portrait of naked ambition that is given in the characters of Macbeth and Lady Macbeth. In today's world, getting ahead is as important as it's ever been. The cases of Enron, Tyco, and other corporate crimes show that people are willing to sacrifice their morals and break the law in order to advance their careers. The Iraq War and the billions looted and mishandled is another example of how greed and a lust for power are still powerful motivators.