Yeah, after Stalin, it's better looked at as a one-party state rather than as a dictatorship in the proper sense. The state and Communist Party bureaucracy were institutionally fused, and the actual distribution of power was often variable within that- Stalin's "Red Tsarism" being an exception rather than the rule, even if Brezhnev did attempt a rather feeble return to the days of the personality cult- so it's hard to generalise beyond saying that the party-state bureaucratic elite, the nomeklatura, held collective political power. You could arguably describe that as a "party dictatorship", although I think that this would tend to imply an autocracy which wasn't for the most part available, with even the nomenklatura finding themselves frequently constrained by their own regulations. (I mean, even Stalin had to get the order for Trotsky's assination signed off by a number off different government agencies, and while in his case this was merely a formality, it's not had to imagine that a less individually powerful politician would find these to be genuine obstacles.)