MPs rowed over scenes in Modern Warfare 2 in which civilians were killed.
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.
War without limits
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.
Army of Two, Call of Duty 5, Far Cry 2 and Conflict Desert Storm were among the games examined.
The games were analysed to see "whether certain scenes and acts committed by players would constitute violations of international law if they were real, rather than virtual".
The group chose games, rather than films, because of their interactivity.
"Thus," said the report, "the line between the virtual and real experience becomes blurred and the game becomes a simulation of real-life situations on the battlefield."
The testers looked for violations of the Geneva Conventions and its Additional Protocols which cover how war should be waged.
In particular, the testers looked for how combatants who surrendered were treated, what happened to citizens caught up in war zones and whether damage to buildings was proportionate.
Some games did punish the killing of civilians and reward strategies that tried to limit the damage done by the conflict, said the study.
However, it said, many others allowed "protected objects" such as churches and mosques to be attacked; some depicted interrogations that involved torture or degradation and a few permitted summary executions.
The authors acknowledged that the project was hard because it was not clear from many of the games the scale of the conflict being depicted. This made it hard to definitively determine which humanitarian laws should be enforced.
It also said that the games were so complex that it was difficult to be confident that its testers had seen all possible violations or, in games in which they found none, that no violations were possible.
24, The Game
Army of Two
Battlefield Bad Company
Brothers in Arms - Hell's Highway
Call of Duty 4
Call of Duty 5
Close Combat: First to Fight
Conflict Desert Storm
Far Cry 2
World in Conflict
Frontlines: Fuel of War
Ghost Recon Advanced Warfighter
Hour of Victory
Medal of Honour Airborne
Metal Gear Solid
Soldier of Fortune
Tom Clancy Rainbow 6 Vegas
Tom Clancy Splinter Cell Double Agent
True Crime Streets of LA
It noted that, even though most players would never become real world combatants, the games could influence what people believe war is like and how soldiers conduct themselves in the real world.
It said games were sending an "erroneous" message that conflicts were waged without limits or that anything was acceptable in counter-terrorism operations.
"This is especially problematic in view of today's reality," said the study.
In particular, it said, few games it studied reflected the fact that those who "violate international humanitarian law end up as war criminals, not as winners".
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."
John Walker, one of the writers on the Rock, Paper, Shotgun games blog, said: "Games really are treated in a peculiar way."
He doubted that anyone would campaign for books to follow humanitarian laws or for James Bond to be denounced for machine-gunning his way through a supervillain's underground complex.
He said the authors did not understand that gamers could distinguish between fantasy and reality.
Said Mr Walker: "For all those who mowed down citizens in Modern Warfare 2's controversial airport level, I have the sneaking suspicion that not a great deal of them think this is lawful, nor appropriate, behaviour."
Jim Rossignol, who also writes on Rock, Paper, Shotgun, said there was scope to mix real-world rules of war into games.
"Whether or not the rules of war are included in the game should be based entirely on whether that improves the experience for the player," he said.
Mr Rossignol said there was plenty of evidence that gaming violence is "fully processed" as fantasy by gamers. Studies of soldiers on the front line in Iraq showed that being a gamer did not desensitise them to what they witnessed.
He added: "Perhaps what this research demonstrates is that the researchers misunderstand what games are, and how they are treated, intellectually, by the people who play them."