Seven Samurai
You really can see how so many things come from this film. Nevertheless, it was a hard slog for the 3 1/2 hours and didn't live up to my lofty expectations. I'll give it another go in about three years; hopefully I see it differently.
I don't think I'll ever understand how this film could be considered a hard slog, the writing and characters are so strong, but I'm sorry you didn't like it more. Not to try and talk you out of your opinion, but if you're not very familiar with this period of Japanese history, you should read
this Criterion essay. I loved the movie even without the historical knowledge, but I've certainly come to appreciate it more by understanding better the important underlying themes Kurosawa uses.