I think it’s pretty uncontroversial that the USSR ended on a low note. Decades of economic isolation by western powers, constant conflict with the usa, loss of faith in the government through some of the destalinisation measures and liberalisation of the economy all took their toll. If history had gone a bit differently and revolutions elsewhere hadn’t been stamped out paving the way for the rise of the Nazis and the ascension of the USA on the back of nuclear horror things might’ve gone a lot better.