In many ways, yes. After the fall of Wuhu in December 1937, for instance, an American missionary reported: "During the first week of occupation, the ruthless treatment and slaughter of civilians and the wanton looting and destruction of the homes of the city far exceeded anything ever seen in my 20 years experience of China... Probably conditions in Wuhu have been less severe than in most places because there was little fighting here. The soldiers seemed especially to seek Chinese women for violation and the saving of these women became one of our major activities over a period of several days... I have kept in constant touch with the Japanese military authorities and the Japanese Consul who recently arrived... They assure me their soldiers are forbidden now to molest the Chinese or to force them to serve them, and most of the officers desire to prevent these offences. In spite of these promises, it is still not safe for any Chinese man and much less for a woman to go on the street..."

After the fall of Kaifeng in June 1938, another observer wrote: "Women dare not go on the streets as they are attacked even in broad daylight in their homes, or dragged off the street to their homes by Japanese soldiers. I never guessed I would ever come into contact with such awful wickedness that is occurring day by day. Multiply anything you have heard about [the Japanese] by twenty and it is only half the truth. Small boys are kidnapped and along with young women are shipped by train to the east..."

That same month, Lieutenant General Okabe Naosaburō (chief of staff of the North China Area Army) concluded that more "comfort stations" (military brothels) were needed to prevent further violence against Chinese women and thereby improve relations with the civilian population, though the Central China Area Army had already set up comfort stations for its units in December 1937. These measures apparently had little effect, however, despite several later attempts to impose harsher punishments for rape. In his 1940 pamphlet entitled "Plan for Improving Discipline," Kawara Naoichi of the War Ministry acknowledged: "Even though there has been an increase in the overall number of soldiers, the ratio of crime can be seen to have increased. From the outbreak of the China Incident to 1939, 420 men were punished by courts-martial for plundering or for plundering accompanied by rape resulting in death; 312 for rape or for rape resulting in death; and 494 men for gambling. Beside these we find other case of violence, incendiarism and murder inflicted on the Chinese." And these numbers only reflect cases that were actually investigated.

Beginning in July 1941, in response to military operations by the Chinese Communists, the North China Area Army initiated a brutal counterinsurgency campaign that entailed the destruction of all villages suspected of harboring guerrillas (sometimes relocating the inhabitants) and the wholesale confiscation of food and crops. Although the Japanese authorities characterized their measures as a "Three Prohibitions Campaign"--"admonishing the Chinese not to burn, commit, crimes, or kill," according to historian S. C. M. Paine--they were known to the Chinese as the "Three Alls": kill all, burn all, loot all. Indeed, when the policy received official approval from Emperor Hirohito on December 3 (as Imperial Headquarters Army Order Number 575), its stated purpose was to "strengthen the containment of the enemy and destroy his will to continue fighting." In the end, the Japanese reign of terror caused immeasurable suffering for the civilian population and an estimated 2.7 million deaths, but it did effectively limit the Communists' ability to mount further offensives. By the end of 1942, the Red Army had been reduced from 500,000 soldiers to 300,000.

Following the Doolittle Raid on April 18, 1942, and after Chinese civilians and soldiers had rescued the crashed American pilots, the Japanese army initiated vicious reprisals and destroyed Chinese-occupied airfields in Zhejiang and Jiangxi. Chiang Kai-shek was forced to commit thirty-four divisions to fight elements of the 11th and 13th Armies, and both sides suffered tens of thousands of losses. Claire Chennault reported: "A quarter-million Chinese soldiers and civilians were killed in the three-month campaign. The Chinese paid a terrible price for the Doolittle raid, but they never complained." But Chiang, who had received no prior warning about the raid, did protest. In an angry message to George Marshall, he wrote: "The Japanese slaughtered every man, woman, and child in these areas--let me repeat, every man, woman, and child."

As they did at Nanjing, the Japanese army regularly executed Chinese prisoners of war. Many captured soldiers were simply dubbed "bandits" and killed on the spot. Others served as slave laborers, and countless perished toiling under appalling conditions. The most unfortunate became human guinea pigs for biological experimentation. At the end of the Second World War, the Japanese apparently held only 56 Chinese in custody.

There are other actions that may or may not be construed as war crimes. On numerous occasions, the Japanese army utilized poison gas (known euphemistically as "special smoke") and tear gas against Chinese troops, all of which required explicit authorization from the Imperial General Headquarters. In 1938 alone, poison gas was employed 39 times in Jiangxi and 21 times in Henan, while in March 1939, Lieutenant General Okamura Yasuji of the 11th Army deployed over 15,000 canisters of gas in order to improve the morale of his soldiers and give them "the feeling of victory." Sometimes the Emperor himself personally approved requests to deploy poison gas, though he evidently forbid its use against Western forces. The Japanese also experimented with biological warfare. In 1942, for example, they attempted to spread anthrax, plague, typhoid, and cholera in Zhejiang province by having aircraft drop infected fleas and having soldiers contaminate water supplies. However, the Japanese suffered 10,000 casualties after their soldiers were inadvertently exposed to the contagions.

The Japanese also employed terror bombing against Chinese cities, mainly Chongqing, Chiang Kai-shek's wartime capital. Between February 1938 and August 1943, Japanese bombers dropped roughly 21,600 bombs on Chongqing, resulting in an estimated 35,000 casualties (with 15,000 deaths). As most structures were built of wood and bamboo, incendiary bombs left large swathes of the city in ruins.

Finally, the recollections of former Japanese soldiers often attest to widespread atrocities. According to one: "Massacres of civilians were routine. They cooperated with the enemy, sheltered them in their houses, gave them information. We viewed them as the enemy. During combat, all villagers went into hiding. We pilfered anything useful from their houses or, in winter, burned them for firewood. If anyone was found wandering about, we captured and killed them. Spies! This was war." And another: "On the battlefield, we never really considered the Chinese humans. When you're winning, the losers look really miserable. We concluded that the Yamato race was superior."

In the immediate aftermath of the conflict, the Nationalist government of China calculated 3.7 million military casualties (not exclusively deaths, it seems) and 9.1 million civilian casualties. On the other hand, pre- and post-war records suggest a 16-18 million loss in population. The war also produced over 95 million refugees, though the status was not necessarily permanent or long-term for every person.

Japanese war crimes is an enormous (and politically and emotionally sensitive) topic, and I've tried my best to summarize important details here in relation to your question. This information comes from my notes, gathered from a wide range of sources, and I will be happy to supply citations if you need them. I unfortunately don't know whether Wang Jingwei and other collaborators ever protested to their Japanese overlords. I hope you find this helpful nonetheless! :)