A leftist Soviet coalition government - i.e. the initial alliances between the Bolsheviks and the Left SRs, some Mensheviks and the Makhnovist Anarchists being maintained - would greatly help making the USSR less oppressive.
It is the contention of Victor Serge that the dissolution of the Soviet Alliance was the true beginning of the drive down the path towards Stalinism. "The end of the Soviet alliance produces in its’ wake a formidable concentration of power. Up till this time, the dictatorship was in a way democratic; constitutional forms were spelt out within its structure. The multiplicity of local activity, the existence of parties and groups, the demands of public opinion, the democratic traditions of revolutionaries trained in the school of Western democracy, and the weakness of the central authority all worked in this direction. The debates within the Bolshevik party, too, have shown us the vitality of its internal democracy. But everything changes at this point. The Allied intervention, striking simultaneously with the rebellion of the kulaks and the collapse of the Soviet alliance, poses an unmistakable threat to the survival of the Republic. The proletarian dictatorship is forced to throw off its democratic paraphernalia forthwith. Famine and local anarchy compel a rigorous concentration of powers in the hands of the appropriate Commissariats. The catastrophe of the transport system compels a recourse to draconic methods of authority on the railways. The war, the total encirclement of the revolution and the inadequacy of spontaneous foci of resistance compel the establishment of a regular army, to supplement and supplant the guerrilla formations. Bankruptcy compels the centralization of financial policy. Conspiracy compels the introduction of a powerful apparatus of interior defence. Assassinations, peasant risings and the mortal danger compel the use of terror. The outlawing of the Socialists of counter-revolution and the split with the anarchists and Left S-Rs have as their consequence the political monopoly of the Communist party and the extinction, for practical purposes, of the constitution. With the disappearance of political debates between parties representing different social interests through the various shades of their opinion, Soviet institutions, beginning with the local Soviets and ending with the Vee-Tsik and the Council of People’s Commissars, manned solely by Communists, now function in a vacuum: since all the decisions are taken by the party, all they can do is give them the official rubber-stamp." -
https://www.marxists.org/archive/serge/1930/year-one/ch08.htm
In truth the Left-SRs as a party were a fluid, nebulous organisation which remained closely linked with the greater SR organisation and had only really existed for a few months before October. In order to create a Left-SR organisation you would need the Left-SRs to emerge as a distinct party long before October in order to truly provide a counter-balance to the Bolsheviks. Considering that the Bolsheviks went from a party of a few thousand to the strongest party in the Soviets, I would say that the conditions of Russia would definitely allow such a possibility. I had a rough plan regarding a continuation of the Soviet Alliance which would start with having Mark Natanson and a section of the SRs in Switzerland arrange with Lenin and Fritz Platten to get the same train through Germany as the Bolsheviks. The reality of the situation of the Russian exiles returning to Russia was that there were three 'sealed trains' through Germany from Switzerland with Natanson getting on the second train but people only remember Lenin's because it was used as 'proof' of Lenin's links with German imperialism.
Thus during the chaotic events of the July Days the accusations of Lenin as a German agent are muddied and it also distances Natanson from the SRs earlier. Maybe the process of sharing the train journey with Lenin also develops a situation where Natanson and Lenin are more willing to communicate and work together. Regardless, it leads to a situation where the Left-SRs split from the main SR party sooner and thus are a distinct organisation when the preparations for the Constituent Assembly are arranged and firmly established as a party when October comes around.
The situation in the Soviets would immediately be different. The Bolsheviks, whilst probably remaining the most energetic and organised grouping, would have to temper their actions to take into account the Left-SRs straight away. It would potentially lead to a different relationship with the peasantry - the Bolsheviks felt, in the crises immediately following the revolution, that grain requisitions were a necessity in order to supply the cities. The Left-SRs protested these harsh measures, laying the groundwork for their break with the Bolsheviks, but in this scenario the Left-SRs actually have the power to do something about it. I could potentially see a situation of the urban worker soviets developing a trade system with the peasant soviets - a system that happened in real life but that the Bolsheviks distrusted due to its nature as petty profiteering leading to state requisitions. Perhaps this would lead to a co-operative style trading system or perhaps it would collapse into famine like the Bolsheviks' policy but regardless it would be a sharp difference to the OTL origins of the Bolsheviks' harsh relationship with the peasantry.
Then we have the Constituent Assembly elections. With the Left-SRs as a distinct organisation, it's potentially very likely that the Soviet Constitution gets ratified in the opening sessions of the CA. Even the anti-Bolshevik scholars of the CA admit that the SR voting block would have been split if the Left-SRs had been a distinct party. The Bolsheviks and the Left-SRs together, even giving conservative estimates, could have had a majority in the CA elections. This situation could have led to the maintenance of the CA as a legislating organisation distinct from the soviets with little power (as power shifted to the soviets where the Soviet Alliance would have had more control). Although it would have been largely superseded by the Soviet Congresses, the CA would nonetheless act as a counter-balance somewhat to the Bolshevik concentration of power we saw in OTL. It would have also shot any talks of 'legitimacy' from the right-wing SRs out of the water - potentially it could have seen other grouping like the Mensheviks as 'willing' to work more with the Soviet Alliance as well (potentially leading to an interesting situation in Menshevik Georgia).
The linchpin of the break in the Soviet Alliance was the Brest-Litovsk treaty. Ultimately the situation on the front was untenable and the Russian army was dissolving through desertion and a lack of supplies but the Bolsheviks almost voted in support of a revolutionary continuation of the war - if the regular army dissolved, the left communists wanted to engage in guerilla warfare which was a similar position to the Left-SRs who felt the treaty was making the soviets the puppets of Germany. Maybe the negotiations go differently with the power-bloc of the Soviet Alliance adding more weight to the negotiations thus leading to a peace treaty far more favourable than Brest-Litovsk. Maybe there's enough support for a continuation of the war on revolutionary terms that we have a tentative resistance to German occupation - this situation would be interesting as it would have kept the Soviets in the same camp as the French and British as 'co-belligerents' of a sort, potentially preventing Allied intervention in Soviet Russia. It would have also cut into the support of White reaction as many joined the Whites thinking that the Bolsheviks were essentially giving up Russian territory to the Germans. Ultimately, it could have led to a far different Civil War where a more stable soviet government would have been able to assert its power sooner.
Regardless of how these events play out it's clear that one thing would have happened if the Soviet Alliance was stronger and remained. The concentration of power into a single-party state could never have occurred and there would have been more democratic checks and balances to prevent any single individual accumulating power. The regime would have been more stable, had more 'legitimacy', and would have potentially had more organisational weight to prevent some of the elements of the famine and dissolution of the state mechanisms that caused so much chaos in the early years following October. This leads to an entirely different political situation in the Soviet Union and it would have been an environment that would never have allowed the likes of Stalin to rise to power.