You should binge them all. The 27 of them (the 26 of Shintaru Katsu, whih depict a young-ish Ichi, one year less young per movie (30-ish to 50-ish), and the Takeshi Kitano movie, which depicts a very much older (white-haired older), considerably more jaded Ichi, the only Zatoichi movie besides Katsu's that actually feels like it belongs.