First of all, this film is a sequel to Hitokiri (1969). Thats one of the classic Samurai swordfighting films with very fast action scenes thats still better than much we get to see today.
"Izo" starts where the first film ended. The protagonist is crucified for his crimes that he committed as a hired terrorist in the service of those who tried to restore the old regime.
But he finds himself alive again, at first not understanding that he has taken on a demonic existence because his soul cannot rest and he must descend through the layers of hell in full consciousness.
Following his motto from the first film, "Divine punishment", he sets out to take revenge on the world and on the gods for getting him into this whole mess.
This film may be another blood bath, but the philosophical content is also enormous. Miike film-making at its very best, another no-budget production whose profundity may give the watcher stuff to think about for years.