Every fan of movies should see a Kurosawa, and this is (along with Yojimbo) the most accessible of his many great works. The film is an artistic and technical masterpiece, but above all it is a rousing adventure story, gripping and emotionally involving from the start. The origin of the film lies in an idea for a story Kurosawa had about a samurai who made a tiny mistake and went home and committed suicide. Told this wouldn't work, he and his writing team began researching the 16th century, and became interested in the fact that villagers would hire samurai as night guards to protect them from bandits, the samurai receiving food and lodging in return. This evolved into Seven Samurai, Kurosawa's greatest jidai-geki (period drama), about desperate peasants who turn to professional warriors when bandits repeatedly raid their harvest.
Kurosawa draws fantastic performances from his cast, most notably Takashi Shimura (as the samurai leader Kambei, the living embodiment of the samurai code) and Toshiro Mifune (as the peasant turned warrior, Kikuchiyo), and marshals the elements for an astonishing climactic battle scene in the mud and the rain. This ten-minute sequence has to be seen to be believed; the images have a painterly quality (Kurosawa trained in western-style painting) but are also extremely realistic, perfectly capturing the chaos of the battlefield as figures wade through the mire, hacking at each other. I've heard it remarked that this sequence was in Spielberg's mind when he conceived the Omaha Beach landing scene in Saving Private Ryan; and indeed, the use of grainy film stock, the slightly speeded-up movement and fast editing, and the depiction of war as utter chaos all seem rooted in Kurosawa.
A final word: do not be put off by the 190 minute running time or the fact that it is subtitled. Although Kurosawa has the reputation of an auteur, he was also a brilliant and influential storyteller. This is perhaps the most entertaining great movie ever made.