Hoss does his best to help a behemouth outcast shake his anger and lead a productive life.
Gene Coon wrote a nice script for this one, admittedly a take-off on "Of Mice and Men" and even the movie version of "Frankenstein" but a good episode nonethleless. The titanic fight between Hoss and Arnie is exciting, though it could be shortened by a minute or two and be better. There is not a lot of time devoted to Leonard Nimoy's character at all, he's slimely but its hard to see his motivations. The saloon girl falls in this category as well, her game of using people and constantly flip-flopping her attitude doesn't make the most sense.
Still, the good things of "Bonanza" dominate this episode, Hoss and his devotion to his friend, Ben and Hoss struggling to find a plan to bring Arnie in after he goes on a murderous rage, a tragic backstory for Arnie. Its a bit obvious but a lot of care is invested in establishing a similarity and bond between the big men Hoss and Arnie (the "Ape").
Installments like this are not too dated and tell good stories that still work for the viewer in a modern context.