I take an issue with the word "failure" in this context. What did the soviet socialism fail to do? Conquer the free world, as the US propaganda claimed? Perhaps, but was it it the true goal of the system?
If we assume, otoh, that the purpose of the system was to speed up th emodernizationa process and to reduce the human cost ofthat modernization, soviet socialim was quite successful in it. All former-soviet block countries, which at the beginning of the 20th centure were ages behind Western Europe, today are on a similar level of development. And the human cost? I think it was overall lower than the cost of slavery, the "satanic mills" and colonial exploitation than was the price of Western Europena and US development, but it was particularly low in Eastern Europe FSU is a different story - the high human cost was caused by multiple factors, most of which can be grouped unde the rubric "Asiatic mode of production" (for the lack of a better term) rather than "state socialism." Stated differently, similar human cost would have been incurred even if history took a different turn, and state socialism asw e know would have not been implementred in Russia.
In sum, I think of the soviet socialism as cast and crutches - you certainly cannot run in a race while wearing them, but wearing them will enable you to run in a race one day. And the pain that you experience is caused mainly by your broken bones, not by the cast and crutches. With that in mind, soviet socialism worked better for Eastern Europe than US-style capitalism for Latin America. Today, Eastern Europe is joining the EU, while Latin America is sliding into neoliberal chaos.
Wojtek