Brilliant acting by Mifune and veiled anti-capitalist themes make this a masterpiece of the "Samurai Movie" sub-genre. There are so many tensions: corruption vs morality, greed vs self-sacrifice, samurai order vs gangster chaos, even the sword vs the gun. It's hardly a surprise when the streets are eventually filled with dead bodies!
The directing by Kurosawa is geared towards building up the tension that often explodes into violent action sequences. There are several dark humor moments that illustrate the cynical attitude of the main character, but also remind the viewer that above all, he is a pretty decent man. The action scenes from Yojimbo have been duplicated endlessly by action movie directors ever since - especially the iconic arterial blood spray.
I would recommend this classic for anyone, as it is one of the more accessible foreign films around, and has a remarkably modern anti-hero as the catalyst.