I aimed at the public's heart, and by accident I hit it in the stomach.
-- Upton Sinclair
The Jungle is one of those books with a reputation -- you can't read it without comparing the book it is with the book you expected. In the case of The Jungle, I expected a heavy-handed Socialist propaganda story mixed with a horrifically shocking description of filth being sold as food. It didn't exactly meet my expectations on either count.
The part about food preparation was disgusting, to say the least. Yet, strangely, it didn't shock me that much because I'd already heard about the worst parts before (the rotten meat coated with rat-dung getting thrown in to be sold as food and treated with chemicals to remove the stench, etc.).
Also, the story was more interesting than I expected. The socialist part is there, to be sure, but interestingly it's just at the end. Essentially, the story stops and then we're treated to a three-chapter discourse on Socialist theory, including a big plug for the Socialist newspaper that commissioned the work. It's like you're reading along then all the sudden it's "...and now, a word from our sponsor." Note that the discourse is about what today we'd call Communism (a command economy), not the modern usage of "Socialist" (which has come to refer to an economic strategy that uses both public and private organizations).
Up until that end bit, however, it's a living, breathing human story. Jurgis starts out with hopes, dreams, and ambitions; with a family and responsibilities. Through the course of the story, we see all of these things stripped away from him and more. The stress of the family's precarious position is almost unbearable as they struggle not to lose their investment in their house, and are fighting for their lives not to lose the basics of survival: food, clothing, shelter, and emergency medical care. Once that struggle is lost, Jurgis's life as a penniless hobo is comparatively simpler, despite his grief at the loss of his wife and son. Sinclair seemed to be demonstrating that "freedom's just another word for nothing left to lose," until, sadly, even that turns out to be false. Before the end, Jurgis loses every shred of decency and self-respect that he'd once had, going from having nothing to having less-than-nothing. A family member (who ends up as a prostitute) matter-of-factly sums up their mutual lesson: "When people are starving, and they have anything with a price, they ought to sell it, I say."
Sinclair did an amazing job of covering every single option that was available to Jurgis, from all different types of factory work, to migrant labor, to petty crime, to organized crime (political graft), to begging. And the reader can understand why Jurgis took each step and how he felt and how he changed. Sinclair -- despite the fact that he himself didn't have the limited options of an unskilled Eastern European immigrant -- shows remarkable empathy. In that sense it's like Zola's Germinal and unlike Uncle Tom's Cabin (where the author is horrified by the cruelty the slaves endure, but really only relates to the free, white characters).
Even though Sinclair explicitly aimed to illustrate the cruel injustice of Jurgis's plight, it's not a simplistic black-and-white caricature. For example, during the meat-packers' strike (which I gather Sinclair passionately supported), his protagonist (Jurgis) is a scab, and the reader still sympathizes with him and his plight. Sinclair really captures the complexity of the problems the unskilled immigrant laborers faced, which is why -- aside from the end -- the story isn't reduced to the heavy-handed propaganda and moralizing you normally get from ideologically-centered works.
That's also the reason the end part is so jarring: The problem he portrays is too complex to be neatly wrapped up with a simple solution.