A "lurker" recommended this report by Ash Carter, ex-Defence Secretary, published by the Belfer Center in October 2017.

Link to a two page summary:https://www.belfercenter.org/sites/d...ager%20web.pdf

The full report:https://www.belfercenter.org/LastingDefeat

He refers in July 2015 to:
Intelligence on ISIS was almost entirely lacking—we did not understand who our enemy was, where he was, or what he would do next.
This seems an odd statement:
Iran has had virtually nothing to do with the liberation of Iraqi territory, and every Iraqi can see that.
A lengthy passage on Turkey and then this, not very diplomatic:
Regrettably, the Gulf countries have so fall fallen short of doing what they can. (In contrast) Singapore and Malaysia joined the counter-ISIS coalition: Singapore’s highly professional military contributed imagery analysts and an aerial refueling tanker to the fight in Iraq and Syria; and as a majority-Muslim nation, Malaysia’s public embrace of the fight against ISIS had major significance.