First off, without the atomic bomb Japan is unwilling to surrender and Operation Downfall takes place in the Fall of 1945. It runs into Japan's Operation Ketsugō which is designed to inflict maximum losses on the invasion. The battle of Japan would have been total war on a level never seen by mankind before. Even the conquest of Nazi Germany would not have compared to it.
Civilians would have been used even if unarmed. Chemical and biological weapons would have been used. Prisoners would not have been taken. Japan still had over 10,000 planes available and the plan was to use them as kamikazes and direct their attacks against transports.
And the US would have fought on and refused to accept anything less than unconditional surrender. Before the invasion began the government considered the possibility that there would never be a formal surrender by the Japanese and were fully prepared to conquer the entire country if need be.
The Soviets declare war and invade Munchukuo. They will conquer Manchuria, Korea, and much of northern China. There will be no division of Korea and no Korean war. Fearing Soviet influence over all of China US forces invade and conquer southern China, French Indochina, and Formosa.
The war in Japan is gruesome and drags on until the fall of 1946, there is never a formal capitulation by the Japanese who fight (almost literally) to the last man. The US suffers over one million casualties including more than 450,000 deaths. It is estimated that over 80% of the entire Japanese population dies during the fighting. Having paid such a cost the US will NEVER permit an independent Japan to exist again. Japan is made a US territory and slowly rebuilt. In 1976 it becomes the 51st state.
In China the Soviets support a more pliable Mao while the US supports Chiang Kai-Shek.
In Europe the final borders are similar to OTL. With the US still fully engaged in the Pacific and the British exhausted, there is a much greater need to rearm at least some German units as a counter weight to the Soviets. Fearing a Soviet invasion the US does not demobolise following the end of the war with Japan. Though extremely unpopular with the American public fear of communism keeps large US forces in both Europe and Germany.
Stalin always looked to take advantage of weakness and would think Allied forces to be weak. In June of 1948 World War III begins over control of Berlin. It is just an excuse, Stalin believes he can conquer Europe and so invades.
The Soviets have an advantage in number of troops and especially in number and quality of armored units. West German soldiers using American equipments fight alongside American, British, and other NATO troops. The Allies are able to wrest control of the air and have complete control over the sea. NATO forces are however at a disadvantage on the ground and driven out of west Germany and into Belgium and northern France before finally halting the Soviet drive. The Soviets are halted thanks to reinforcements from the US and logistical problems caused by air attacks on bridges and railways.
In China the US has the advantage. US and nationalist Chinese troops begin to liberate northern China.
Under blockade and air attack from B-52s as well as from missiles the Soviets begin to struggle and beginning in spring of 1949 begin to be pushed back. The war ends in 1952 with NATO forces approaching Warsaw. Stalin suffers a 'heart attack' and the new Soviet government calls for an armistice.
Germany is reunified under a democratic government. Poland and the remaining Eastern Block remain Soviet. In the east China is also one nation with a pro US government as is Korea. Manchuria is divided between the USSR and China.
There is no Cold War but there are a series of small 'Hot Wars' afterwards. The USSR is less aggressive but still supports other nations. The US and its allies follow a theory of 'non appeasement' and 'open intervention' and are much more willing to act militarily in any country that looks to be about to go Red.
For instance, when Castro became a bit too openly socialist US Marines and Army soldiers invaded in 1961 and installed a new government. This became a common occurrence throughout the twentieth century.