Well first of all, the actions of Japanese troops (and later civilians) were viewed thru the lens of contemporary racism. John Dower's "War Without Mercy" documents the racist propaganda of the time and it's impact on wartime atrocities. This means that actions that might be viewed as "courageous" by European troops could be viewed as "fanatical" by Japanese troops. (as an aside though, Nazis were often demonized by propaganda as fanatical as well.)

However there was also real a difference in the brutal conduct of the Pacific war that is not just a matter of perception, and was largely a function of the institutional culture of the Japanese Imperial Navy and Army. Japanese troops were slow to accept surrenders and rarely were surrendered en mass by their commanders even when little military purpose to resistance remained. Last ditch charges like the last banzai charge on Saipan often left few survivors of Japanese garrisons. Japanese soldiers and occasionally civilians also frequently committed suicide rather than surrender. In contrast, Allied troops did surrender when resistance became futile, for example at Wake Island or Singapore. German troops surrendered in Tunsia and even grudgingly at Stalingrad. Once the reluctance of Japanese troops to surrender became known, Allied troops became less likely to seek surrenders and the Pacific war became a totally merciless racial war, culminating in Okinawa and the bombing campaign against the Japanese home islands.