He certainly had a lot of enemies, and very few allies at the end. So he might have been. At any rate, he didn't die a day too early, and if he was assassinated the culprit did the peoples of the Soviet Union and Eastern Europe, who suffered under his brutal cruelty, a huge favour.
He was certainly a madman, but when he took power in the late 1920s, the Soviet Union was a backwards agrarian nation, torn by war, in a world of modern industrial states. When he died, it was a mighty imperial superpower controlling half of Europe, with ideological influence over nearly 1/3 of the world population, possessing atomic and hydrogen bombs, the best airfighters in the world (MiG-15 and MiG-17), the largest land army, and within 4 years of overtaking the U.S. to launch the space race. Yes, he was terrible, but from a realpolitik perspective he was quite successful. This is his biggest difference from Hitler, who left his country amputated and partitioned.
Edit: And the amazing part of it is that all of this he achieved despite having virtually the entire class of talented party members shot, as well as half his country scorched during WWII.
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