Cuba. Despite a continuing embargo from one of the largest economies on the planet, and the collapse of its greatest allies over two decades ago, socialism in Cuba has eradicated homelessness and illiteracy, produced one of the best internationally-recognised healthcare systems on the planet.
If we lift the restrictions of "a few decades", you'd find that the USSR transformed a feudalist, barely-electrified nation into America's greatest opponent on the world stage, with a stake in the space race, in less than half a century.
Cuba is comparatively an incredibly poor nation that has missed many advancements of modern society in recent decades. Wages are dirt low, access to the internet is low, and from what I gather, access to modern anything in general is challenging. There are no great advancements coming out of Cuba. I don't consider that a success, I consider that a failure. I don't want to stop progressing or move backwards into a deep maintenance mode as Cuba has.
Are great advancements the measurement of good? Is progress for the sake of progress so great? To me, it's a question of the proverbial slaves building the pyramids: it's easy to insist that society should work for the improvement of technology if your quality of life is already secured by the people below you on the ladder.
You may not want to stop progressing, but ask Americans without healthcare coverage whether they would prefer government money going to research or to providing for their needs, and many of them will disagree with you.
I have been to Cuba. In my experience, that's not an accurate description of their homes. And "deep poverty" is a meaningless statement in a country as different as that - despite a lack of wages, Cubans are well-provided for by the government, which is more than can be said of a good part of population in many Western nations.
>USSR never managed to turn to US greatest opponent
This is a very interesting take on world history. What do you consider the USSR's role in the world to be during the Cold War? What makes you reject most modern historical thought?
And there are those in the West who starve. Who better provides for the poor?
>And USSR's role was the same as North Korea today
The US is not currently producing a huge amount of propaganda in a culture war against North Korea. There is no scare of North-Korean-sympathisers infiltrating American society, or its government. The West is not fighting any proxy wars with the Koreans, nor are they engaging in international competitions equivalent to the space race. There is no "North Korean sphere" - North Korea has no cultural or political influence over a broad group of nations around the world. North Korea does not constitute some kind of "fourth world".
Please, show me one country not rooted in capitalism which has "succeeded impressively" in recent decades.