He was mostly alright, but his significance really comes from popularizing and formulating what is now known as Marxism-Leninism.
As a result of mounting internal and external pressure, as well as the power-struggle following Lenin's death, Stalin had to make countless concessions to deal with problems that could not be avoided.
Because of his role leading a country that was led into, and greatly harmed by war (tens of millions of deaths as a result), it can be very challenging to get an appropriate critique and analysis of his role. You are not going to find any example of peaceful revolution, nor will you find any examples of countries in a state of war that can grant complete freedom and liberty.
I defend him to the extent that he led a struggle against European fascism, and I defend him against accusations that Marxism and fascism are the same. Going so far to condemn Stalin generally has a tendency to grant a certain level of forgivenes and apologia for fascists and their collaborators, as well as a wide assortment of reactionaries and nationalists.
When it comes to people who would be identified as "Stalinists", usually what is meant is something more similar to what we would call National Bolsheviks (NazBols). If not that, then in reference to the tendency of certain Marxist-Leninist groups to justify social conservatism, petty nationalism, and premature centralization.
One thing I'd like to touch on: the experience of the Bolsheviks told us that we need unity of Marxists, where we exclude the distorters of Marx. If you want to be a Marxist, you need Marx - no way around that. Stalin had to read Marx's major works, Lenin did so and more, and so did Trotsky, Luxembourg, even Kautsky and Bernstein.
Any major revolutionary figure is going to be smeared and distorted for someone else's gain. People still hate Robespierre, for instance, and people still try to rewrite the narrative of people from Nat Turner to Huey P. Newton - Stalin was no different. You don't have to defend him at all, nor do you have to condemn him (or any other historical figure), but you should at least understand the real Stalin and understand that the USSR was born out of the ashes of the Russian Empire - generally for worse as we came closer and closer to its dissolution. If you don't care to catch the full story, you are going to be clueness when it comes to any revolutionary movement across the Americas, especially the US. You can try to overcorrect or overly emphasize how much you don't like Stalin, if you'd like, but remember that Stalin's opposition and the leftists who opposed the initial October Revolution were well on their way to make mistakes in the complete opposition direction - equally as harmful and destructive. That doesn't make you superior, it makes you blind. Stalin's errors were far from the only possibility.
It could've went way worse, or it could've been far better off - which would you prefer?