The atrocities committed by the Japanese are indeed tragic. I recall reading about the so-called "Rape of Nanking" in college, and also about the harsh punishment meted to Allied POWs in Southeast Asia- some of it at the hands of Korean officers (Korea was a colony of Japan at the time).
Your mention of the horrendous treatment of Korean women is also another example of what might be considered a war crime.
Some will argue that crimes committed in war should live simply in the vacuum of war; they should be relegated to the farthest reaches of one's memory, if not forgotten. Yet we can never forget Hiroshima, Nagasaki, Buchenwald, Auschwitz, Dachau, Dresden, Stalingrad, St. Petersburg, Nanking and so many horrors that are now so familiar that they are known merely by the names of their locations.
In this day and age, it would be fitting for countries to at least formally recognize the extent of the horrors that were committed by national leaders that represented them. Some nations will clearly feel uneasy offering a formal "apology"; there might be some justification in the claim that the crimes of the NAZIs are not to be stamped upon the souls of all Germans. Yet to sweep crimes under the rug is to do an injustice as well. Nations must in the very least acknowledge the extent of the brutality that the actions of their leaders caused during WWII.
Offering a formal apology would be even better. I don't think that by doing that, a nation would embarass itself. On the contrary, it would show that the past can never be forgotten, but a better future may still lie ahead.