This is a massive question that's been picked over by historians, polemicists and historical polemics for almost a century now. Unsurprisingly, I'm not going to provide a conclusive answer or go into great detail. That would require contributing yet another book to the debate. What I will do is give a quick summary of the factors that led to the 'degeneration' of the revolution, based on your criteria. Feel free to ping me with specific questions after that.

But first, the question of 1917. I disagree with /u/llamastingray in that I strongly believe that we can talk of degeneration: that is, the ideals of the revolution, and those who advocated it, 'degenerated' into what a party dictatorship in a matter of years. This assumes that there was something to retreat from in the first place.

Far from demonstrating a lack of popularity, the Constituent Assembly elections show that the Bolsheviks were almost the uniform choice of the Russian working class (the only constituency that they ever really cared about) and did surprisingly well amongst soldiers and the peasant communities in the north-west. See the events in October proper: the Bolsheviks were by some distance the best represented party at the Second Congress of Soviets that ratified the seizure of power.

So whether or not Bolshevik popularity was fleeting, or whether people wanted an exclusively Bolshevik government, there can be little doubt that the overall emergence of a Soviet government had a popular basis. This was borne out by subsequent events: the Bolsheviks could simply not have survived through coercion alone. Not only did the revolution spread independently of Bolshevik channels but time and time again the Bolsheviks would be saved by the fact that they represented 'Soviet power'.

But to pull ourselves back to 1917, I strongly agree with the revisionists who argue that Bolshevik success in that year was a product of of their structure (an 'open democratic party', Fitzpatrick) and the degree to which their policies aligned to the popular aspirations of the workers. To quote Adam Wildman:

...the workers developed their own self-awareness, definition of goals and intensity of action, which, reversing the conventional equation, reshaped the Bolshevism of 1917. The Bolshevik Party succeeded in forging firm links to the working class in 1917 because it articulated and promoted this 'conciousness' more vigorously than its rivals, and in the process it reabsorbed something of the proletarian ethos.

This is why Bolsheviks came to play leading roles in not just the soviets but also trade unions, factory committees and (in the north-west) soldiers' committees. In 1917, unlike 1922, it's possible to talk of 'Bolsheviks' as comprising a broad pro-Soviet movement, one that included Left SRs, Left Mensheviks, anarchists, etc. The question really is why, five years later, had the latter been subsumed by the Communist Party and the Soviet state? Unfortunately the easiest way to tackle that is to look at what drove the new regime's actions post-October.

Bolshevik Ideology

The first question is of course whether the revolution actually degenerated at all. Some would argue that the Bolsheviks achieved exactly what they set out to. That's something I strongly disagree with: not only was policy often an ad hoc reaction to events (I went into detail yesterday on an example here) but key aspects of the Soviet state, such as the fusion of party and state, emerged entirely unplanned.

More to the point, the Bolsheviks themselves fully aware that things had not gone to plan. Lenin's later writings (eg Better Fewer, But Better) are fairly scathing on the deficiencies of the Soviet state and the various internal 'oppositions' don't need much introduction. Zinoviev would have spoken for many Bolsheviks when he plaintively mused in mid-1918: "Sometimes it seems that this is not it, that perhaps this is an enormous historical misunderstanding that we are taking something else for socialism."

But. While the Bolsheviks may not have been "jackbooted proto-Nazis" (to quote David Renton), we shouldn't ignore the role of ideology. Whatever the dire circumstances that faced them - and, as per below, it was pretty dire - the Bolsheviks' reactions were governed by some ideological baseline. Centralisation, technocracy, anti-market policies, retention of Tsarist 'specialists', reliance on administrative measures or coercion, etc... these were the tools that the Bolsheviks reflexly fell back on. Personally I'd ascribe this more to the holdover of Second International thinking than some inherent 'hardness' but it was present.

Russia's Backwardness

The Mensheviks had infamously taken the standard Marxist line that Russia was simply not ready for socialism. Lenin, in maintaining the need for an interim 'state capitalist' period, didn't break as sharply from this as is often made out. Both however were overtaken by events: how do you construct a workers' utopia in a peasant society?

Even if we leave aside both theoretical squabbles and the Civil War, the fundamental problem that confronted the new Soviet state from its inception to the early 1930s was simple: the peasantry. Ironically, it was the peasants who had emerged the strongest from the workers' revolution. The Black Repartition had effectively eliminated large-scale commercial farming and severely reduced the flow of grain to the cities. Just feeding the urban population was a pressing concern of the state for decades. This sapped Bolshevik efforts to expand Russia's industrial base and modernise the country.

All the major phases in the early Soviet period (War Communism, NEP, Stalinism) are in some way an attempt to deal with that key question. How to balance industrial development (believed to be integral to creating socialism) with placating the peasantry? This remained a millstone around the new regime's neck. The relatively small size of the working class also had the knock-on of severely limiting the manpower pool that the Bolsheviks could draw on to tackle the below crises.

This could be ignored in the initial post-October flush (when anything seemed possible) and faith could be put in the wider European revolution. The debates of the 1920s groped towards a theoretical solution that didn't accept that the Mensheviks might have had a point, ultimately producing 'Socialism in One Country'.

[Continued below]

First things first: the October Revolution of 1917 wasn't really a grassroots revolution. While the toppling of the tsarist autocracy in February was popular throughout the Russian Empire, the Bolshevik assumption of power in October was not. They were able to take power largely because the reputation of Russia's Provisional Government (who took over the task of governing after the tsar's abdication) had been so damaged by months of inaction and scandal that many citizens were no longer willing to defend it. While politics had been radicalised, and the Bolsheviks enjoyed mass support, they were by no means the most popular party in the country - in the elections for the Constituent Assembly, which had been planned before the October Revolution and took place in November, they completely failed to get a majority. Outside of Petrograd, the capital, the Bolsheviks had to fight to take key positions of power - even in Moscow, their takeover faced strong resistance. So, while soviets were springing up around Russia during 1917 and while the workers' movement was growing, it's important that we don't merely assume that these phenomena represent widespread support for the Bolsheviks.

Next: practical circumstances. Following the Bolshevik assumption of power in October 1917, the country soon devolved into Civil War. The Bolsheviks, confined to a central area of the country, were fighting counter-revolutionary forces on multiple fronts. To actually be successful against the Whites, the Bolsheviks needed a well-disciplined army and a productive industrial centre. Elections of officers in the army, workers' control of factories, and many other popular initiatives of the early days of the revolution were scrapped. A number of the 'utopian' ideas discussed and practiced in the early days of revolution proved impractical in the running of a state, and had to be scrapped. Industry, and a significant amount of society, became militarised. The Bolshevik leadership argued that this was necessary in order to win the Civil War and secure the victory of the revolution for the proletariat, but that didn't mean that by the time the Civil War was ended that popular initiatives were reintroduced. In fact, the end of the Civil War signalled a tightening of Bolshevik control over society, with the subordination of the independent cultural organisation Proletkult to the state, the 1921 ban on factions within the Party itself, and the suppression of the Kronstadt Uprising.

You've already highlighted Bolshevik ideology, and that certainly was important in establishing an autocratic style of leadership early on in the Soviet regime. The Bolsheviks viewed themselves as a revolutionary vanguard, whose role was to lead the workers forward into Communism. This advance to Communism was a historical necessity, as dictated by Marxist historical dialectics. Even when they enjoyed widespread support, the Bolsheviks never thought of themselves as being shaped by any popular movement: their role was to guide the workers toward Communism, nothing more and nothing less. They viewed themselves as the true leaders of revolution, and believed that they understood the needs and the interests of Russia's working classes better than the working classes themselves. As for the 'backward' nature of Russia - the general lack of education and such only helped sustain the view that the Bolsheviks were the people who had to guide Russia out of its current 'darkness.'

You'll notice that, so far, I've neglected to mention Stalin. The things I've previously discussed were elements of the Soviet political system and political culture which allowed for the development of an authoritarian style of leadership. Stalin was a very astute player in the power struggle which developed after Lenin's retirement from active politics in 1923. Naturally, further changes in the political system and culture of the Soviet Union occurred during the 1920s and 1930s both before and after Stalin's rise to power. I don't want to imply that Stalinism was the natural outcome of the revolution, but by 1921 the Bolshevik Party had set itself on an authoritarian path, influenced by both practical circumstances and ideology - a path which obviously helped the emergence of a single, authoritarian leader after the death of Lenin.

Sources:

• Christopher Read, From Tsar to Soviets

• Rodger Pethybridge, The Social Prelude to Stalinism

• E. H. Carr, The Russian Revolution from Lenin to Stalin

As a somewhat related side-note, J Arch Getty has recently published a book called Practicing Stalinism, focusing on the Stalin period, which argues that in a number of essential ways Russian political culture has remained similar for centuries; that the Russian state has always been governed by kinship groups and patronage - that Stalinist autocracy is not so different to the autocracy of tsarist times. It's an interesting premise, and you may enjoy reading it - but I would warn anyone that the book has a number of faults, not least Getty's use of gross oversimplifications and misinformation to prove his points. If you want to read it, I'd approach this book more as presenting an idea for discussion than anything more factual or set in stone.