Many people here will defend that "Stalinism" doesn't exist because it's not fundamentally different from Marxism-Leninism, it just happened so that the USSR during Stalin times had to live through some of the worst moments in recent European history, facing a war that murdered 20+mn Soviet citizens, so the country took desperate measures at times.
In my subjective opinion, Stalin was probably a good revolutionary communist who was completely devoted to socialism. From a young age he rejected his comfortable studies as a priest and became a worker agitator, full-time revolutionary during a time where that would land you in jail (he spent years in jail at Siberia as a consequence).
He constantly risked his freedom and his physical safety for almost two decades during Tsarism with no other incentive than the betterment of the life conditions of others, for example if he just wanted money he could have kept the money that he stole when executing the 1907 Tiflis bank robbery instead of giving the money to the Bolsheviks to further revolution, and he lived a comfortable but modest life as a leader, without much in the way of luxury other than the occasional holiday visit to party-official-exclusive dachas.
During his mandate, the USSR managed to industrialize enough to first defeat Nazism (saving tens of millions of lives in Eastern Europe from extermination) and then to eliminate hunger in the eastern block (saving tens of millions more in my opinion), while being the first country to provide universal healthcare and education at no cost.
Flagrant mistakes were obviously made, such as the deportations of Crimean Tatars or Koreans within the Soviet Union, or arguably an excess of repression during the peak of the Gulag system in the eve of WW2, though this latter effort was far from centralized and indeed the central government of the USSR imposed maximum incarceration and execution rates that the smaller republics had to request permission to exceed. These failures must not be hand-waved to "Stalin was just bad", they're actual serious policy errors that proper communists take seriously and analyze in their context in order to be able to learn from them and not repeat them, instead of just saying "I'm a better person than those who gave everything during tsarism for the betterment of the peoples' living conditions".
And boy did these conditions get better. Life expectancy skyrocketed after 1945 all over the eastern block, which would otherwise have been colonized and exterminated by Nazis in a similar fashion to native Americans by the US colonization that inspired Hitler, socialism saved HUNDREDS OF MILLIONS of lives from starvation, genocide, colonization and mass deportation.
All in all, I think he was a good guy who genuinely cared about the betterment of the rest of peoples' lives, though a flawed individual who had to live through some of the hardest responsibilities in the hardest times of human history. As a last note, he's not responsible for everything good nor for everything bad that happened in the USSR, that's big-man-theory version of history and that's idealist nonsense. The material and historical conditions led to the decisions made by the people and by the party, many of which directly contradicted Stalin and passed anyway.