I expect a lot of that has to do with the fact that Soviet operations against Japan went for about three weeks: August 9th - September 2nd, although fighting was mostly over by the 20th. Most broad English works covering the Pacific War do mention it; but the standard narrative generally runs like this, "The US, unprepared for war, is hit by a surprise attack. It then gears up and completely smashes Japan, leaving it a smoldering wreck." Pearl Harbor and Hiroshima make great narrative bookends. The Russo-Japanese War of 1904-1905, the border conflicts of the 1930s, and the Manchurian War of 1945 all distract from that primary narrative. Also the fact that Soviet archives used to be off limits to western historians, meant there was a significant lack of primary sources. That is changing as over the past 25 years or so such sources have become more available.

So that covers the why you probably haven't read anything on it.

The campaign itself was a masterpiece of Soviet style warfare, taking advantage of all they had learned from four years fighting the Germans. The Soviets had almost a 2:1 advantage in men: 1.6 million vs 0.9 million. Most of the Japanese and Manchurian forces were also much less well trained and equipped. The soviets had over a 5:1 advantage in artillery, and in excess of a 2:1 advantage in most other weapon categories. Most Soviet equipment was also qualitatively better as well. So the Japanese forces were thoroughly outclassed.

The Japanese weren't necessarily surprised. They were aware of troop build ups. And the Soviets had withdrawn from their mutual non-aggression pact. But they weren't prepared for the size or tactics of the Soviet forces. The Japanese had expected a Soviet invasion to focus on the rail line from the border to Harbin and then on to Port Arthur. That was done, by the Soviet 2nd Far East Front. While these armies engaged the Japanese head on, the Soviet 1st Far East Front and the Transbaikal Front swooped in from East and West behind the Japanese cutting off supply and retreat to Korea. The Soviets largely avoided head on attacks on pockets of strong resistance. Dividing and surrounding the Japanese they had reached the Chinese coast by the 20th. They also conducted a series of amphibious assaults in Korea on the 18th further preventing the Japanese from falling back in good order. In theory the Japanese surrendered on the 15th. In practice orders to surrender weren't understood or ignored and most major groups didn't actually surrender until the 20th. Fighting continued in places up until around September 2nd.

While this was going on they also grabbed all of Sakhalin and ran a series of amphibious assaults down the Kurils.

This map gives a pretty good high level overview of the campaign.

There's one excellent source I'd recommend for further information, David Glantz' The Soviet Strategic Offensive in Manchuria, 1945: 'August Storm'