The answer is they are somewhat faithful, but not completely trustworthy. I remembered the book as primarily being about the struggle between anarchism, socialism, and Stalinist Communism; that does form the backdrop for many of the events, but for the most part there are only brief references throughout the narrative portion of the book. Orwell makes a point of how irrelevant the political disputes seemed to his experiences at the front, which make up most of the pages of the book. The final chapters in the book give a more focused treatment of the parties and their alliances and betrayals, but never really dives into the ideologies of each faction.
Looking back, I think that reading this book probably prompted me to go off and do additional research on the war and its combatants from other sources; this was in the dark ages before Google or Wikipedia, so I would have combed the card catalog to find another book or two in my high school library. If memory serves, this may have led into my senior-year self-study program on revolutions, which led to some cool research and papers on the French Revolution, the Haitian Revolution and (I think) the Spanish Civil War.
On a personal level, I used to be a rather bloodthirsty young jingo, cheering on America's first invasion of Iraq during Operation Desert Storm. Around this time I was converting into a pacifist, recoiling at our bombings of Serbs during the conflict in Bosnia-Herzegovina; if I didn't already identify as a pacifist, this book probably nudged me further in that direction, as it gives a decidedly unglamorous look at war. Orwell writes more about trying to keep warm at night, foraging for firewood, battling public lice, or eating moldy bread than he does about actual combat. Most of his existence at the front is marked by boredom, toil, and frustration than by fear. When combat does occur, it is exciting but not heroic. He misses his shot, or his gun jams, or some other problem occurs. In later actions he probably kills people, or at least wounds them, but can't be sure: there's a rolled grenade in the dark and a bang and a cry of agony.
Overall, Orwell's attitude towards war seems to occupy a middle ground between Hemingway's grim-but-necessary view and Vonnegut or Heller's war-is-a-meaningless-absurdity takes. Orwell hates war and finds it ridiculous, but he nevertheless feels compelled to fight. He writes "When I joined the militia I had promised myself to kill one Fascist — after all, if each of us killed one they would soon be extinct." It's tempting to view Orwell as an idealist, with his commitment to worldwide revolution and his personal sacrifices, but he's really endlessly making the best of the bad choices before him. I'm somewhat reminded of Bonhoeffer's tormented decision to commit the sin of murder, not believing that it could be justified or excused, but because his conscience demanded it.
You can see Orwell's thoughts on the importance of freedom versus authoritarianism crystallizing during his experiences and being formalized in this book, and they will be presented memorably in their final form in 1984. Homage to Catalonia is a bridge book between his earlier socialist books like Down and Out in Paris and London and his anti-Soviet Animal Farm and 1984. I think it's important to see him as a democratic socialist and not as a liberal: he's on the side of the (self-organized) workers, not the (authoritarian and democratic) police. As he writes, "I have no particular love for the idealized 'worker' as he appears in the bourgeois Communist's mind, but when I see an actual flesh-and-blood worker in conflict with his natural enemy, the policeman, I do not have to ask myself which side I am on." It seems like Orwell's experience of Communist propaganda that distorted and lied about things he directly experienced was what pushed him over the edge into direct opposition to that party.
As a young man, and a libertarian, I embraced the 1984 version of Orwell. I believed that the worst things a government can do is suppress free speech and disseminate falsehood; the solution was to prevent censorship and get the government out of media. As an older lefty, I now see censorship as just a single aspect in a complex problem. The real problem is people not knowing the truth, whether they're consuming the propaganda of Alex Jones lying about Sandy Hook victims, or embracing the delusions of QAnon, and more speech has certainly not dissuaded the masses from massive delusions. I increasingly want to shut down propaganda, or make it harder to find, and get infuriated when corporations like YouTube and Facebook start algorithmically driving victims towards radical falsehoods.
Several years ago I started watching Tropes vs. Women in Video Games, and YouTube's algorithm kept encouraging me to watch hateful misogynistic videos; the algorithm had been hijacked by alt-right provocateurs, but as YouTube is directly profiting off of video views it has an obligation to stop that manipulation. Years later, YouTube continues to funnel young men down a right-wing rabbit hole that leads from debate videos to white-supremacist propaganda. It's a different problem than what Orwell was writing about, as the world and media are more fragmented today, but individuals can do more damage: a single man with a machine gun can wound 800 people in Las Vegas, a single Twitter feed can destroy a reputation or incite a massacre. Orwell's views evolved over time based on what he saw in the world, from Burmese imperialism to London poverty to Soviet show trials, and I'm curious what he would make of the 21st century. Ultimately he always comes down on the side of the people, not as abstract units of political power but as breathing, passionate people who enjoy good food and tobacco and comradeship and sunsets. Honestly, I imagine that he'd feel more comfortable battling the techno-capitalist powers of 2019 than he was fighting intra-left disputes in 1938.
One particularly amusing, albeit potentially "problematic", aspect of this book is Orwell's constant stereotyping of Spaniards. He dryly notes how his life was saved many times thanks to the poor marksmanship of his enemies and his fellow-militiamen. He creates a national character and consistently applies it to all Spanish people in the book: they are unfailingly friendly, lazy, good cooks and enthusiastic eaters. This is a recurring tic of Orwell, who similarly presented the French in Down & Out as smelly and unsanitary, and the Germans as efficient, and the Italians as emotionally demonstrative. All of these stereotypes ultimately reinforce Orwell's own Englishness: despite his professed commitment to global solidarity, he fundamentally is, well, kind of a hobbit: fussy, proper, aghast at poor manners and hygiene, suspicious of other cultures but ultimately buoyed by inner determination and practicality.
The book as a whole kind of reminds me of Nick's disclaimer in The Great Gatsby that he is one of the few honest people he knows. Orwell is trying to be truthful, and openly admits his biases and limitations. He tries to be dispassionate in how he writes about his personal experiences and carefully separates this from the chapters that were built on his research and conversation with friends. All of this gives him a lot of credibility when he then looks at the official reporting and propaganda to come out of the war. We believe him, as he's shared ample criticisms of the POUM and isn't aggrandizing his own stature. I'm left with more admiration for him than ever before: at his courage and sacrifices, and at retaining an open heart and clear eyes, able to grow and change based on the evidence of what he saw.
There were lots of great quotes in this book, but here are a couple that I bothered to jot down. Page numbers from the 1955 Beacon Paperback.
"It was like an allegorical picture of war, the trainload of fresh men gliding proudly up the line, the maimed men sliding slowly down, and all the while the guns on the open trucks making one's heart leap as guns always do, and reviving that pernicious feeling, so difficult to get rid of, that war is glorious after all." - p. 192
"It seems to always be the case when I get mixed up in war or politics - I am conscious of nothing save physical discomfort and a deep desire for this damned nonsense to be over. Afterwards I can see the significance of events, but while they are happening I merely want to be out of them - an ignoble trait, perhaps." - p. 212