Throne of Blood is not Kurosawa's best movie - or even his best samurai movie - but it is a superb adaptation of one of Shakespeare's best-known plays, Macbeth. In fact, even with the vast number of times filmmakers have taken the Bard's plays and morphed them into different times and settings for the big screen it's hard to think of a better one.
So much of this comes from the core performances in the film that it's easy to overlook Kurosawa's craft. Toshiro Mifune verges on (and often achieves) iconic status in every role he played for Kurosawa, but his performance as Washizu aka Macbeth is an obvious stand out, both for its complexity and the fact that the film almost entirely revolves around him. But he is matched by Isuzu Yamada as his wife. Lady Macbeth is one of the juiciest roles in all of Shakespeare (and arguably all of English theater), and Yamada shows why here. Her machinations are so coldly logical and yet diabolical that it's hard to tell if she truly believes what she is saying or she is propelling her husband toward death through her own thirst for power. The combination of the conventional feudal Japanese female demeanor and the Lady Macbeth persona is an especially chilling one, bringing something intellectually unique to a role that has been endlessly explored as a representation of femininity (or at least the male perception of it).
Kurosawa's hand still manages to impress, though. He is at his flashiest when he needs to be, like in the moody scene in which Mifune encounters the spirit or the flat and striking compositions that enclose Mifune at his celebration as he begins to lose his mind. Throne of Blood was made at the height of Kurosawa's career, with Criterion entries Rashomon, Seven Samurai, and Ikiru behind him and Hidden Fortress, Yojimbo and The Bad Sleep Well still to come. This confidence shows in the straightforward way he presents the material here, but he can also sometimes be too acquiescent to the source material. This is where the film fails to transcend its stage roots (something which would prove to be a crucial flaw in Kurosawa's next film, The Lower Depths). The final death scene, too, is so over the top (and vaguely reminded me of the absurdly long horse scene in his later masterpiece Kagemusha) that it nearly turns to parody - saved only by Mifune's complete disappearance into his role.
I think it says something remarkable about Kurosawa as a filmmaker that this movie ranks somewhere in the upper-middle of the pack for his films. Taken on its own, Throne of Blood is a superb film, better than 95% of the movies released this year (even that is probably a conservative estimate). Within Kurosawa's (and Mifune's) catalog it's just another classic, even if it's essential viewing as Shakespeare on film.