The last of the volumes. More essays than letters, and even the essays are less personal and more political. Communism, which was a thread throughout the first three, really comes out in full force.
Still some primary source with interesting tidbits, like asking a correspondent whether he's torn up his ration book for clothes, and recounting how people don't really believe it. (They went off clothes rationing in 1949.)
Also stuff about hunger in Europe after the war, objecting to some nasty post-war trials, discussing Communist atrocities and how they were not to be discussed.
Essays on writing in general -- this is where "Politics and the English Language" appears -- and on various authors, sometimes vitiated by his blindspots (they can be amusing insights into Orwell, to be sure). Though at one point he observes that a book that opposes you makes you angry which is hard to see around, he doesn't observe that it is also likely to come across as falsified. (Socialist Realism is bad not only for the lack of conflict, but because it assumes the collective action problem out of existence, and beings without the collective action problem aren't human.) Actually, I think his best is his essay on Tolstoy's attack on Shakespeare because there he comes to grip with the ideas and argues with them.
He wrestles with the Soviet views on literature and at one point observes he can feel more sorry for the persecutors than their victims because the victims at least have the clarity of knowing what is going on, where the persecutors are shocked and bewildered and unable to fathom why providing the best of everything to writers nevertheless does not produce the literature they desire. (Despite his Socialism, Orwell realizes that writers, at least, need some freedom to produce.)
He also had a bad shock from the atom bomb, which appears to have seriously shaken his views on progress. Nevertheless, he keeps arguing from the assumption that historical inevitability exists, and that he can discern it. I wonder how his views would have changed if he had lived to see the effects of the welfare state and the fall of Communism.