The movie seems to revolve around the irony that while Gennosuke, the main character who is basically cast out of society in to the wild and forced to constantly fight for his survival like an animal, is actually the only character that tries to show any qualities above that of a beast.
Every other character from a group of bandits he encounters to the group of clansmen trying to exact revenge after Gennosuke killed their leader, to a man and his wife from a separate clan trying to steal gold to improve their clan status are either acting for revenge, power, or greed. The greed exists because most of the movie takes place around a mountain where gold has just been discovered and Gennosuke is befriended by a poor man hoping to find some for himself.
Throughout the movie there is constant backstabbing, deception, and generally brutal acts committed by a multitude of these characters. For instance the man from a separate clan living with his wife on a shack by the river are attacked by bandits in the woods trying to steal the gold they have already mined; they hold the wife hostage in demand for his booty but the man would rather give up his wife then part with his gold. Her saving grace is when Gennosuke shows up on the the scene and acts with the courage and compassion to save her life. The husband does come around a little later in the movie but in the end his rival clan plans to kill everyone on the mountain and save the gold for themselves threatening the couple, Gennosuke, and his persuers.
Gosha does a great job with his imagery, demonstrating a wild, dark world threatening to swallow humans whole. Throughout the film, which is almost all outdoors are scenes of men disappearing into woods or buried beneath shrubbery. In fact, it's quite reminiscent of another Japanese Classic, Rashamon. Some of the shots are virtually identical, ie the sun being concealed over the forest canopy or disappearing behind a mountain.
One of the best touches is towards the end when soldiers from the rival clan are planning to take the mountain, and kill anyone who knows about the gold. One of them sounds a battle horn to signal the approach, a battle horn made to sound conspicuously like some kind of strange animal call.