Most (all?) of the originals are available as part of the Criterion Collection now, which is awesome. I actually saw a western recently called Red Sun that starred Charles Bronson and Toshirō Mifune, sort of a crossover between the two genres that was pretty entertaining. Mifune played a lot of samurai roles including at least one Zatoichi film I know of.
I'm a big fan of Takeshi Kitano's Japanese gangster movies, and he didn't do a bad job reprising the role of Zatoichi relatively recently, but for me the film overall sort of suffered from the same problem I pointed out about modern western movies. :-(
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