Structural Issues
The real problem with Rashômon lies in its structure. The movie's structure relies on having the same story retold by four different people. This yields interesting results because we are allowed to learn about each character's concerns and feelings through the version they relate. I don't really know whose story comes closest to the truth, but the last story, told by an unbiased witness to the drama, is the most powerful. The principle emotion expressed in this film is shame. In so far as the movie expresses how shame cripples humanity, it is incendiary.
My rating: 9
If the movie had ended in the forest after the final fight between the samurai and the bandit, then I would have rated it a 10. Initially I believed Kurosawa did not end the film there because he found the message too bleak. But now I believe that Kurosawa was hindered by the movie's structural reliance on unbiased observers. He began the movie with the unbiased observers, and to end the story without returning to them would felt unbalanced or poorly executed. So he elected to return to the unbiased observers in order to tie up his loose threads. That makes sense, I would have done the same thing. The problem is that the unbiased observes are unbiased: by their very nature, they lack inner conflict integral to the story: they're boring. Kurosawa tries to mend things by plopping a symbol of humanity (the baby) in their laps, but the effort comes off as heavy-handed. As a result Rashomon's cleverest feature, its conflict of narrative, becomes its Achilles heel.