A Great Place to Start
To assess the state of an issue you have to understand the issue, and with intelligence issues at the forefront of the national agenda these days, both current and former practitioners once again find themselves wishing that someone would take the time to educate both those who should know better (e.g. the overseers) and the shake-and-bake "experts" amongst the commentariat. While there is no shortage of books on the intelligence business, there are not a lot of good primers on the business writ large (hence the need for most college-level instructors requiring the purchase of 2-3 different books).
That changed recently with the release of Confrontation or Collaboration: Congress and the Intelligence Community by Harvard's Belfer Center for Science and International Affairs. Authors Rosenbach and Peritz have crafted a concise piece of work that addresses the major issues in a fashion that isn't at all cursory. Of particular value is the sources section (at the end of the PDF or after each discrete entry on the Web site) which provides those who are into details and background a healthy list of resources to drill into.
Originally crafted for members of congress, this is a publication that anyone with an interest in US intelligence should review. It's the primer I'd try to make if time allowed, but it doesn't and I'd probably not do half as good a job.