USSR:
Basically, the Russian leftist coalition holds together in 1917 and accepts the initial offer of peace at Brest Litovsk,which involved Russia keeping Ukraine and possibly also Finland, Moldova, and part of the Balkans. (OTL, Lenin wanted the coalition to accept the peace, but many in the coalition did not, leading to the fracture of the coalition, and the Germans would go back on the offensive and take Ukraine and other territories too after the failure to agree to the initial Brest Litovsk offer). Due to the earlier German exit from the east front, and the leftist coalition sticking together rather than descending into infighting, the Russian civil war is shorter and less devastating (the leftist coalition has less need of implementing harsh "war communism", and the famines of 1921-22 are either lessened or don't occur at all, with the shorter war having less of a harsh impact on peasant agricultural production).
The Bolsheviks still end up coming to sort of dominate the coalition and newly forming USSR, but it remains somewhat more politically open and pluralistic. The soviets are somewhat shifted aside in terms of power by the newly forming bureaucracy, but not disbanded or made completely irrelevant, and the ban on factions doesn't occur. The NEP still ends up being the initial policy, and is maintained after Lenin dies, with someone other than Stalin taking power. The USSR is able to industrialize quicker (some suggest that Stalin's brutal methods allowed the USSR to accelerate industrialization, but the industrialization was paid for in no small part due to grain sales, which were significantly disrupted by the rapid collectivization, which here instead is pursued far more gradually over the course of decades, avoiding the disruption and 1932-33 famines), the absence of the Stalinist purges of officers, intellectuals, inventors, and so on lead to a stronger military (with Tukhachevsky remaining in the position to influence military doctrine with deep operations), a more innovative and capable Soviet R&D sphere, and a more vibrant and open cultural sphere. The Stalinist turn towards social conservatism in certain ways does not occur, and instead the USSR remains more committed to social progress (if at times still pursuing it somewhat gradually). The bureaucracy and government is able to evolve in a more constructive direction, facing less of the issues of Stalinist corruption, repression, and ossification. The USSR of the 30s and 40s retains aspects of authoritarianism, but is rather more open compared to OTL, potentially being described as a hybrid regime, and the government pursues a slower transition to socialism (along the lines of the idea that a developed capitalist state is needed before a transition to socialism, one of the OTL criticisms of the Stalinist era), and without the issues of the Stalinist era, is able to remain more committed to that goal over the longer term future (as opposed to something like China under Mao, where the attempts at rapid socialism under Mao led to disaster and were followed by what could arguably be seen as essentially a political rejection of any substantial intention to build socialism as opposed to just an authoritarian nationalist state with a veneer of socialist rhetoric)
China:
Things also go differently in China. In OTL, the CPC and KMT were allied until the late 1920s when Sun Yat Sen died and was succeeded by Chiang Kai Shek, a right-winger who broke the United Front and sought to eliminate the Communists. The KMT had both rightist and leftist wings, so let's say that factional matters go differently somehow and instead of Chiang Kai Shek taking over after Sun, some leftist does. And the CPC sort of takes the dominant position in a United Front with the left-wing of the KMT, and perhaps some other factions like the Guominjun. Perhaps this would result in some rightist-nationalist uprisings and conflicts against the leftist Nanjing government analogous to the OTL communist uprisings and conflicts against the rightist Nanjing government, but perhaps the status of the left controlling the KMT, along with populist appeals of the united front to the peasants, are able to minimize or avoid any significant anti-left uprisings. Here, the communists, in power earlier and without having been cut down by the fighting with the nationalists and having been taken over by Mao, end up basically imitating the new Soviet government, in pursuing NEP-like policy, as opposed to the ineffectual policy of Mao and the Great Leap Forward, so China avoids the issues of the great famine, and, similarly to the USSR here, remains more open and more consistently dedicated to socialism in the long term even though it starts off with a more gradual approach. The Soviets, seeing a fellow socialist government in power in China as opposed to the rightist KMT of Kai Shek in OTL, begin sending somewhat more economic and military aid in the late 20s and early 30s, which further helps cultivate relations between the two states.
Perhaps the Chinese, playing to the United Front/KMT rhetoric and pointing to their own NEP, are able to at least at first sort of give the appearance of playing all sides against each other, lobbying for aid from the US, UK/France, and Germany as well. Also appealing to the US with the open door policy, and appealing to the US and UK/France with the potential to be a counterbalance to the Japanese Empire. Which could maybe give the Chinese an additional boost at the start here.
The Mukden incident still occurs, with the Japanese making sizable initial gains and pushing warlord Zhang Xueliang's Fengtian Army back. But Nanjing government here isn't busy playing whack-a-mole with the communists as in OTL, they are able to send the main force of the central government army up north to assist in fighting the Japanese in Manchuria, along with some forces from other warlords. Along with that, perhaps the USSR engages in a bigger Operation Zet, with more resources sent to China, along with perhaps some military 'volunteers' and officers to help. With these additional factors in their favor, the Chinese forces are able to keep the Japanese contained in Manchuria and eventually push them first out of Manchuria and then off the mainland altogether, occupying Korea and setting up an allied socialist state there. Thus the Second Sino-Japanese War occurs earlier, and lasts perhaps one or two years, ending in a Chinese victory.
Europe, 1930s:
With the USSR avoiding the Stalinist path, the USSR and European communist parties end up less oppositional to European social democratic/labor parties, avoiding the 'social fascism' stuff (though there are still definitely misgivings over, for example, the German social democrats suppressing the attempted revolution, allying with the proto-nazi freikorps, haing Rosa Luxemburg killed, and so on). By the early 1930s in Germany, for example, instead of being split two ways between the SDP and KPD, the left is split three ways roughly equally between the SPD, KPD, and a surviving USPD taking up the political ground between them, with all three on halfway decent terms with one another.
This less divided left (well, divided into more factions, but with the factions being less oppositional to each other), however, has an added effect of frightening the political right and center even more. In Germany, despite doing slightly worse in elections, the Nazis still become the dominant power on the right in the 1930s, and the establishment right and center still choose to enable Hitler to take power. We can just sort of handwave/kill butterflies and say that while things go slightly different, Nazi Germany is still able to rise up, and start WWII, taking Austria and Czechoslovakia, and then conquering Poland by late 1939.
In Spain, with the support of a stronger Soviet Union, the Republicans (increasingly being dominated by a coalition of communists, anarchists, and non-socdem socialists as the war goes on) are able to beat the Nationalists.
European War, 1940s:
Perhaps sometime after the Fall of France, the USSR takes the initiative and initiates war with the Axis. Or perhaps they remain in a defensive posture, but whoever is leading at that point is more believing of reports of a German invasion, and thus the initial response isn't so incompetent and disorganized. Perhaps the Soviets keep most of their forces on the alternate Stalin line rather than moving them up after the alternate Molotov-Ribbentrop Pact (or perhaps that pact just doesn't occur). With a more capable officer corps (having avoided the purges), a somewhat more technologically advanced military (due to avoiding purges of inventors, and due to, for example, earlier adoption of-and without the initial bureaucratic opposition to-mass production of the T-34 tank), the avoidance of having much of the airforce destroyed on the ground in the initial invasion (due to a more competent reaction to the war's outbreak), and with a larger base of industrial production and population base (due to a continuation of the NEP and avoidance of the great famine), the Red Army is able to stand up to the Axis, without the massive gains of Barbarossa, and is able to much more quickly take initiative and make advances into Axis territory. Perhaps the war is ended a year or two earlier, and the USSR ends the War on the Rhine rather than where they were OTL.
With no war in the Pacific likely to occur, the US probably remains more isolationist at first, though they may still do lend lease for the Western Allies after mainland Western Europe falls to the Nazis. As the tide of the war turns against the Axis, the US public may become more concerned over the chance of socialist domination of all mainland Europe. Perhaps the US directly enters the war in the later parts, to try and maximize the amount of land under Western Allied control at the end of the war, or perhaps they just stick with considerably increasing their material support for the WAllies, along with still building up their military more, still being concerned for the geopolitics of the post-war era.
With the USSR in a stronger position and acting more independently from the WAllies, there isn't really any equivalent of the Pottsdam conference to determine the postwar borders, so things are rather more tense at the end of the war. With most of the German forces fighting in the east, the UK and French rump based in Algeria (with or without the US directly involved, and possibly leaning more on colonial troops-like the Asians, since territories like India and Indochina won't be under threat from Japan and won't need their troops reserved as much for those areas) make landings in Western Europe at some point, perhaps Italy still flips, and perhaps the Soviets purposely stop at the Rhine to avoid overstretching themselves, or perhaps the WAllies just end up meeting the Soviet forces in their advance around that area.
Postwar, mid 1940s to present:
The Cold War still happens, in some ways different from OTL with more tension, stronger western red scares and opposition to the eastern bloc, and with the Soviets and Chinese never really going through a split, being instead ideologically similar and happy with standing together due to their cooperation in the Second Sino Japanese War and later the European War. The USSR still makes itself the dominant power of the territories taken in Eastern and Central Europe, but governs with a much lighter hand compared to OTL, and focuses rather more on rebuilding the eastern bloc economies as opposed to exploiting them for Soviet gain. Also Yugoslavia is larger (and the Tito-Stalin split doesn't occur), and Germany doesn't lose the eastern territories-apart from East Prussia, which the Soviets spun off into a European alternative to Israel and ended up its own multiethnic state. The Soviets are, in addition to getting Germany up to the Rhine in their sphere, are also able to get Denmark, Norway, and Greece in their sphere. The early years of the Cold War see very high tensions between east and west, but the development of the atom bomb (a little later than OTL by the UK and US, a little sooner than OTL by the Soviets) ends up cementing things in place and avoiding an outright war (the avoidance of a Korean War-type thing also helps temper things somewhat)
Over the course of the later half of the 20th century, the eastern bloc gradually expanded both state-owned enterprises and non-state collectives, to the point where those make up a large portion of the economy by the end of the 20th century. The end of the 20th century also saw the rise of the internet and automation, which offered to give the planned aspects of the economy a significant boost in efficiency along the lines of plans like CyberSyn, which as of the 2010s has been something the eastern bloc has tentatively been experimenting with.
After the European War, the USSR established ComEcon, first as a means to oversee economic aid and rebuilding of the countries of East/Central Europe, which would later expand to also involve developmental aid for China and Korea, as well as the newly emerging socialist countries in the era of decolonization. The ComEcon would expand in its roles as the 20th century went on, sort of like the European Coal and Steel Community and the European Communities, later involving various political matters outside of economic aid. In 1999, the Treaty of Leningrad would be signed between China, Korea, and the Soviet Sphere in Europe, creating the Council for Economic and Political Integration (or ComInteg for short), which would inherit certain roles of the ComEcon but was also founded on the open goal of integrating the various institutions of the member states, with intent for eventual full political union. By present day, Cuba, Nepal, Spain, and Indochina had also joined the ComInteg.
At present, the eastern bloc finds itself still locked in a Cold War with the west, though the Cold War has seen a detente of sorts for the past dozen or so years. The eastern bloc has seen significant reductions in military spending, engaging in recent years in a very large effort to complete the transition to a green economy, and to provide aid to other poorer countries seeking to go green without being impoverished. There is significant debate among the eastern bloc powers on foreign policy, regarding whether aid should be freely provided even to countries with major records of human rights violations, or instead used as a leverage to promote progressive causes abroad, as well as more broadly in regard to the cold war and whether the east bloc countries should play along with the west in the current detente or should be doing more to directly promote revolutionary forces abroad. Debate also exists over intra-bloc and domestic policy, such as in regards to whether political union of the states should be the current goal, vs a more rapid attempt to move to a fully classless and stateless society even with the still considerable opposition by the western bloc.