MITRE tries hard to do the right thing; execution is often lacking as are clear and consistent goals.
Pros
MITRE has some very bright people and has well established position in the public sector. Some of the work is truly fascinating; one has opportunities to parlay technical skills & interests into research programs. Some of the work programs truly make a difference in the world.
Cons
MITRE values work-life balance. However, as MITRE is really more aptly described as a collection of many projects rather than a consistent corporate culture, you may be expected to work long hours, weekends, and holidays depending on the project to which you are assigned. In addition, some of the sponsor set just plain do not like contractors, and show little compunction about publicly berating you. In addition, in recent years many former military have been hired into the company and subsequently promoted too quickly into management and without having been socialized. While some of these people are excellent, many are not. Some dislike civilians and make little attempt to hide their contempt.