Titled Victims, Perpetrators, Assets: The Narratives of Islamic State Defectors, the report relied on published accounts of several dozen people who have left the organisation, including testimony from seven women.
According to the researchers, the defectors who have opted to go public represent just the tip of the iceberg, with the vast majority who manage to leave simply walking away quietly.
Authorities in the United Kingdom estimate that half of the 700 Britons who have left to join Isis have returned to the UK. Of the defectors surveyed by the researchers, two were British.
Some who left were disappointed by the "quality of life" and were "typically among the ones who had joined the group for material and selfish reasons, and quickly realised that none of the luxury goods and cars that they had been promised would materialise".
Power shortages and a lack of basic goods was also blamed, while two said they left after hearing they were to be used as suicide bombers.
"They wanted to first experience fighting and get an opportunity to enjoy the spoils of war before going on their final mission," the report said.
For others their experience of combat "failed to meet their expectations of action and heroism".
The level of brutality against fellow Muslims and infighting were also raised as reasons for leaving.
The report said the defections had been "sufficiently frequent to shatter IS's image as a united, cohesive and ideologically committed organisation".
It added: "They demonstrate that IS is not the jihadist utopia that the group's videos promise; and that many of its own fighters have deep concerns about the group's strategy and tactics."
It suggested the pace of public defections was increasing.
One of the defectors is British widow Shukee Begum, who was stranded in Turkey with her five young children after fleeing Isis when her husband was killed fighting.
But defecting from the group was complex and dangerous, with those who succeed in fleeing the group's territory fearing reprisals or prosecution once they return to their home country, the study said.
It called on governments to do more to remove obstacles that prevent defectors from speaking up, saying their testimony could be help prevent potential new recruits from being radicalised.
The report said: "They joined the most violent and totalitarian organisation of our age, yet they have also become its victims, and their stories can be used as potentially powerful tools in the fight against it."
Russian fighter jets land in Syria, says US
Russia has begun military operations in Syria by sending in 28 warplanes as it becomes more deeply involved in the conflict, United States officials claim.
The officials said 12 fighter jets and 12 close-support aircraft had arrived in recent days at a Syrian airbase in Latakia, where four jets were stationed last week.
Russian drones had also started surveillance flights, the Americans said.
Yesterday Novaya Gazeta, an independent Russian newspaper, reported that Moscow might launch "demonstrative" strikes in support of Bashar al-Assad's embattled Syrian Government in the coming days, before President Vladimir Putin is due to speak to the United Nations General Assembly next week.
The apparent increase in the flow of Russian arms and personnel to Syria has prompted speculation the Kremlin may be preparing for direct military intervention on Assad's side.
Russian military officials have confirmed that they are expanding and modernising a naval base at Tartous and an airbase in nearby Latakia, but have denied plans to intervene directly.
Putin defended the military build-up in a meeting with Benjamin Netanyahu, the Israeli Prime Minister, in Moscow.
Putin said Russia's actions in the Middle East "have been and always will be very responsible". He also insisted there was no threat to Israel from the Russian-Syrian alliance.
Netanyahu said he told Putin that Israel was determined "to stop the smuggling of weapons from Syria to the Hizbollah". Russia offered no opposition to that policy, he said.
The United States believes Assad must go.
Reasons for leaving
• Among reasons given by Isis defectors were:
• The brutality shown towards Sunni Muslims.
• Infighting and behaviours they considered un-Islamic.
• The fact that their duties were "dull" and lacked the glamorous heroics they expected.
• The living conditions and the quality of life.
