I thought it was okay for a Ukrainian man to run around beating people with a bat.
Video games depicting war have come under fire for flouting laws governing armed conflicts.
Human rights groups played various games to see if any broke humanitarian laws that govern what is a war crime.
The study condemned the games for violating laws by letting players kill civilians, torture captives and wantonly destroy homes and buildings.
It said game makers should work harder to remind players about the real world limits on their actions.
The study was carried out by two Swiss human rights organisations - Trial and Pro Juventute. Staff played the games in the presence of lawyers skilled in the interpretation of humanitarian laws.
Twenty games were scrutinised to see if the conflicts they portrayed and what players can do in the virtual theatres of war were subject to the same limits as in the real world.
"The practically complete absence of rules or sanctions is... astonishing," said the study
The authors said they did not wish to make games less violent, instead, they wrote: "[We] call upon game producers to consequently and creatively incorporate rules of international humanitarian law and human rights into their games.