Depends which tendency of Marxist you ask.

There are very few out-and-out Stalinists around these days. People who are prepared to defend the Stalin regime do exist, but in very small numbers, and they're not taken seriously by anyone.

Those who still call themselves Marxists might fall into several camps; Trotskyists, more or less, or those influenced by the "New Left", or (again in very small numbers) some form of Maoism. Very few orthodox Marxists remain.

So, what is the Trotskyist view of the Soviet Union? "Criticism of the post-1924 (after Lenin) leadership of the Soviet Union, analysis of its features and after 1933, support for political revolution in the Soviet Union and in what Trotskyists term the deformed workers' states."

Trotskyism is a variant of Marxism, and, along with anarchism, which is not Marxist, is one of the dominant influences on the left today. Another influence being the Situationist International, also influenced by Marx and also rejecting Stalinist tyranny and the bureaucratic Soviet state, as obviously not being truly liberatory.

Marxism was able to recover from the Soviet experiment for two reasons; 1. There were always anti-Soviet variants of Marxism, right from the start of the Soviet Union, and 2, It was able to sustain a critique of Soviet authoritarianism, bureaucracy, Stalinist tyranny, with a Marxism adapted to current economic circumstances.

Here is a quote from a website, marxistoutlook.com, obviously of Trotskyist tendency: "As we have seen, the Russian Revolution did raise the whirlwind of struggle in the west, but it was betrayed by the social democratic and Stalinist leaders who succeeded in battening onto the working class and sabotaging their revolutionary initiative, hence the second of Trotsky's alternative predictions came true and the revolution was crushed by the imperialist west, although, incredibly and in spite of the continual attacks, the Nazi invasion, blockades and attempts to undermine it, the Soviet Union lived on till 1991 due to the inner strength of the socialised planned economy. But the most important consideration is that Stalinism is now thankfully a thing of the past, it can no longer be an effective tool in the hands the ruling class, a means of subverting the revolutionary struggle. The urgent necessity now is for the working class to build a revolutionary party of the Bolshevik type and to throw off its social democratic leaders, and the path to revolution will be wide open".

Trotskyism was the normal alternative Marxist form for those in the mid and late 20th century who had grown disillusioned with the Communist Parties and Soviet authoritarianism. And by the 1960's there were a lot of such people.

But even if one could still contrive to be a pro-Soviet Marxist as late as 1991, it wouldn't be hard to adapt the Trotskyist viewpoint and express something similar by way of explanation. That is, that the Soviet Union was undermined from without, by liberalising its economy.

For more information on this, you should ask this question on /r/DebateaCommunist. You will probably get much fuller answers than the ones you get here.

Perhaps a better question for also ask /r/AskSocialScience and/or /r/askphilosophy.

The problem with the answer to the question is that Marxism, essentially, is what you make out of it. The most common thought of Marxism today doesn't even adhere to the historical determinism put out by Marx. You have a lot of different and competing thoughts on what Marxism is, how it should be used and what it is worth today.

You really don't have a single authority on Marxism that could be seen as the defining one. Therefore the question asked is coming somewhat to "What is the interpretation of Marxists of the Collapse of the Soviet Union?". It gets somewhat on an individual level as there hundreds of interpretations and views, all somewhat contained within Marxism.

Even the Soviet Union itself lost their definite influence on the left and their interpretation in the 60ies. And since then it has only become more complicated.

You can find answers ranging from a conspirational economic destruction by the West to the Soviet Union was a state just like any other and therefore it doesn't have any bearing on the fundamental idea of Marxism/ Socialism.