It can also mean "one of the greatest" in this context, I believe (my Russian is a bit rusty, to say the least).
But nuances aside, it was indeed one of the greatest catastrophes of the 20th century. It was a disaster for numerous indigenous peoples of central Asia and the far east, who depended on Soviet subsidies. It was also a disaster for many African countries and Cuba that depended on Soviet assistances - for selfish reasons, to be sure, but assistance nonetheless. It was a disaster for Yugoslavia and Iraq, which became easy target of the US "theatrical micromilitarism" (as Emanuel Todd aptly dubs it).
So it was indeed a disaster, especially when you abandon the US-centric perspective. While we are at that, it was also a disaster for the US liberals and left who were crushed by the US corporate right wing juggernaut once it felt "safe from the Soviet threat." Methinks the US lefties and pwogies should go on a pilgrimage to Moscow to thank bat'ushka Stalin for the brief interlude of civil rights and political civility they enjoyed in the 1960s and 1970s, as the US ruling class felt compelled to put their house temporarily in order to stave off the "Soviet threat."
Wojtek