The dude is a flawless film maker who nailed pretty much everything he did.
I've seen every film he's made and if I can make a recommendation it's that you should watch every film he made.
It will be worth your time and effort.
I follow auteur theory and tend to watch everything someone makes if that someone has some skill, it tends to work out. With Kurosawa it works 100%.
A film that you must see of his that hasn't been mentioned is RAN. It's amazing.
My top picks (not necessarily his best films, just stuff that slapped me in the third eye.) oh and it's in no particular order.
Dreams
Red Beard
The Bad Sleep Well
Ikiru
The Idiot
Stray Dog
I live in fear
The lower depths
Like I said everything he did is gold.
Some other Japanese directors to watch.
Takeshi Kitano
Yasujiro Ozu
Yoji Yamada
Kon Ichikawa
Yojiro Takita (When the last sword is drawn)
Takashi Miike
Kiyoshi Kurosawa
Hiroshi Inagaki (Samurai Series)
This is one of my favourite samurai films, it's fantastic. It's also new, relatively. Many of Japan's modern samurai films are really pretty bad.
http://www.imdb.com/title/tt1728196/