I think Stalin was fairly awful on balance and a key figure in the Soviet Union's degeneration into an imperialist oligarchy (albeit a very different sort than the United States was and is).
what? stalin was comparatively more 'conservative' in the soviet sense than most of his major rivals. look at beria.
once he eliminated Trotsky and the "left" the policies he adopted re: collectivization and industrialization were anything but conservative. say from 1928-33.
note the use of the phrase 'in the soviet sense.' bizarrely enough beria was more open to 'liberalization', at least in the sense of more engagement with the west and a return to the relatively more mixed market approach of lenin. stalin might have been a revisionist but the extent is very much exaggerated nowadays