This doesn't quite get the measure of Althusser's relation to the PCF leadership. On a largely philosophical plain he did challenge the extant party philosophy which did claim to be 'marxist humanist'. He argued that this 'Marxist humanism' was coeval with an accomodation to bourgeois intellectuals ('you're humanists, we're Marxist humanists, sign our petition against nuclear war'). But Althusser's was a pose of intransigence. He was only trying to get the party up to speed on the latest in Franch philosophy, which was 'anti-humanist' not 'humanist'. Why bother sucking up to Sartre, when he is old hat, you ought to suck up to Foucault and Derrida instead. Insofar as it was any kind of development, it was a regressive one, and E.P. Thompson was right on this, one that led to a mechanistic and lifeless conception of history, one in which subjectivity is dismissed as an ideological effect of capitalism, which is to say a polemic against the idea that working people make their own liberation.On the meaning of 'Stalinism' as a political category, I insist that this has a specific meaning, and its meaning is the one given it by the person who coined it, Trotsky. Trotsky meant by Stalinism the errors that flowed from the adoption of the anti-Marxist policy of 'socialism in one country', such as the degeneration of the Soviet Union, the western adoption of 'national roads to socialism' and so on.
In that camp that Trotsky called 'stalinist' there were, later on, some critics of Stalin, like Khruschev, most typically, but also Imre Nagy, Monty Johnstone, Martin Jacques and others. They used the word Stalinism in another sense to that which Trotsky used it. They did not accept Trotsky's critique of the 'national roads to socialism'. Rather they restricted their critique of Stalinism to that of his 'cult of personality' and some 'excesses' due to the persistence of 'socialist alienation'. Most of them ended up champions of the free market, or joined New Labour. There were apart from the 'reform communists', Maoists, who adopted a faux radical attack on Khruschev for his policy of cooperation with the West. Some of Althusser's followers became 'Maoists'. Some of the NLR people were sympathetic to Maoism. Maoism burned out pretty soon after Mao made peace with Nixon.
The NLR was in part a reaction against Stalinism. The Communist Party of Great Britain was a staid, if not outright reactionary organisation in the 1960s. It dedicated a lot of its time campaigning against the evils of American comics, and trying to stop rank and file activists taking over the unions. That was why the NLR came into being. Some of the people involved were Trotskyists, like Isaac Deuscher, Norman Geras and Tariq Ali. But Anderson made sure that the editorial board was never beholden to any one party, and kept a number of 'reform Communists' - like Monty Johnstone - involved, as a counterweight to the Trotskyists.
NLR readers were mostly carried away with the Althusser cult. Anderson's criticisms at the time were more muted. But he is right. Althusser was a repulsive shit, whose influence on Marxism, philosophy and radical politics was wholly detrimental.