Militaristic might be not technically correct, it was more of a police state than a military state, after the WWII Stalin put a lot of effort to make sure that military will remain a tool and not have agency on itself. All the police-adjacent organisations though were so powerful that they didn't have to be militaristic to exert all the power.
Everything else is absolutely correct though, complete, absolute power was in the hand of an unelected individual and the people he empowererd, as much as power was concentrated. So as much as authocracy and dictatorship could overlap, USSR was an embodiment of that.