I've been trying to get a grip on the Spanish civil war for some time and having put down at least two other books on the subject, Orwell's very personal account of his part in events made very good reading.
His account reads more like a a letter to a friend than a historical text and Orwell is always ready to admit his true feelings, noble or otherise. In particular his admittance to not fully grasping the political context to the fighting is a humble admission yet reflects the vast complexity of the situation.
My experience of this book may be swayed by reading it at night in the warmth of a caravan in the mountains of Catalonia, with the wind rattling outside, where it's easy to imagine Orwell huddled in a trench desparately trying to start a fire to keep warm and ducking wild shots from fascists huddled in an opposite trench.
His observations of people, events and the genral climate in Barcelona and on the front carry a great honesty and stand as a record of a view of the fighting on the ground. I had to re-read the appendixed chapters describing the politics but Orwell does an admirable job in attempting to explain what is a very complex political situation.