1. Stalinism is a form of statecraft practiced in Russia somewhere between 1924 and 1953. It is a series of policies, some of which ended with Stalin's death, some of which endured. If Stalinism is this and nothing more then it is an historical curiosity.
2. Stalinism is a system of government best described as bureaucratic state capitalism, where the state is fused with the economy but the imperative is capital accumulation. Its value and necessity depends on your perspective. From the point of view of the group effectively governing Russia during the late 1920s Stalinism, as it came to be, was essential and justified. Stalinism was, from the point of view of Russian history, progressive. It made Russia into a modern society. But that's not our perspective. Capitalism is a global system, and was a global system back when the USSR was founded, even back when the Russian Revolution began. Capitalism did not need developing, it was ripe to fall. This has bearing on the 3rd point.
3. Stalinism is a political strategy whereby Communist Parties around the world were effectively agents of Russian foreign policy. This meant different things in different countries. The consistent theme was Russia need to survive and compete within the capitalist world. Though the Communist Party contained many serious revolutionaries it's political strategy was never revolutionary. Without having an Actually Existing Socialism to serve surviving Communist Parties in the core capitalist countries adapted their strategy only slightly, by positioning themselves as left social democrats, to the point where in several countries they are almost the only true surviving social democratic parties, the official social democrats having become social liberal.
4. So, ok, Stalinism is not a strategy for transcending capitalism, why does it matter? Firstly it matters for the simple, ideological point regarding all revolutions leading to tyranny/co-option. Secondly, it matters because the violent intervention from the top of Russian society around 1927/8, which created Stalinism, did lead to significant change. Can change from below compete, full democracy, self-government compete? The fact that the Russian Revolution ended up founding a bureaucratic command economy when it started as an experiment in communal democracy would suggest to some that such democracy is utopian. We can only make extrapolations from the present into the future, but there're three things worth noting:
(i) For centuries now significant mass movements that have challenged the status quo have developed communal forms of democracy, even if only in embryo. Why would a utopia keep cropping up throughout history?
(ii) The development of capitalism prepares us in part for communal democracy. An example; the republican ideal of citizenship, of popular sovereignty (even if deferred to an elected representative) means that each is able, or should be able, to take their place as head of state. This also applies (in an obviously more round-a-about way) to constitutional monarchies.
(iii) It's a sore day for humanity if it's still not capable of liberating itself. Without change from below, at this point in time, human civilisation is almost certainly doomed.
