For fairly obvious reasons, I've got Trevor Aaronson's The Terror Factory: Inside the FBI's Manufactured War on Terrorism on my to-be-read list, notwithstanding this fairly withering review by Ali Soufan, a former FBI Special Agent and one of the primary interrogators of al Qaeda's Abu Zubaydah, among other detainees. The success that Soufan had in eliciting useful information through traditional FBI rapport-building interrogation is recounted in a number of sources, including his own book and Kurt Eichenwald's 500 Days.
An impartial review of the FBI's efforts to fight terrorism after 9/11 would give it high marks overall. It gets hundreds of leads daily, and it has a duty to check them all out, no matter how dismissible they appear. The Iranian regime's 2011 plot to assassinate the Saudi ambassador to the U.S., which was uncovered thanks to a Drug Enforcement Administration informant, is a reminder of why. Unfortunately Mr. Aaronson fails to appreciate this, and instead uses most of his pages to accuse the FBI of entrapment. Tellingly, he notes toward the end that "I am frequently asked why entrapment has never been an effective defense in the terrorism cases. I've struggled with the answer to this question." The answer, of course, is that the evidence shows that these were real threats to the U.S., and we are fortunate that the FBI intercepted them.