(from the McClatchy article)
U.S. troops also are frustrated by the different rules of engagement they must operate under in Afghanistan. Until Jan. 1, U.S. forces in Iraq operated under their own rules of engagement. If they saw something suspicious, they could kick down a door, search a home or detain a suspicious person.

But in Afghanistan, they operate under the rules of the NATO-led International Security Assistance Force, of which U.S. troops are part. Under those regulations, only Afghans can search buildings and detain people.
Since the Law of War, as seen by most NATO nations, tends to follow the path taken by the Eminent Jurists report (discussed in this thread, posts 188-190), there might be more "one hand tied behind the back" in Astan than in Iraq.

On the other hand, US Forces (including USMC) might not find the ROEs a practical problem - adapt, improvise, overcome, etc. So, are the NATO ROEs[*] part of the problem ?

[*] If they are as classified as ours, discussion would have to be limited.