It's a tearjerker. I didn't actually cry, but I love sad stories. More objectively, it's a classic of American muckraking. Specifically, the muckraking concerns the horrible conditions at the Chicago stockyards, the corruption of the meat-packing companies, and the misery of the immigrants who worked there.
I should warn you: the end of the book is ruined by pages of crude political agitprop about how the workers should turn socialist and take over Chicago. (The author, Upton Sinclair, was a well-meaning socialist.)
Best quotation: "For twenty-five years old Antanas Rudkus and his son had dwelt in the forest together, and it was hard to part in this way; perhaps it was just as well that Jurgis had to devote all his attention to having a funeral without being bankrupted, and had no time for memories and grief."