Pros
MITRE focuses very hard to provide employees with a quality work life opportunity. Providing about 5 weeks of annual leave, generous retirement contribution matching, college tuition reimbursement, flexible work hours, there's just too much to name. If you have a family, MITRE is a great place to work for. Over the course of the years, I have seen many people go on to receive their first or second Master's degree while continuing to work full time. The fact that MITRE has such a diverse work portfolio with DoD, IRS and FAA, there's many different types of work that you can get involved with.
Cons
There are many people at MITRE who are knowledgeable in their respective fields. However, that means that a majority of those people are occupying the upper-level positions that others cannot advance to. MITRE typically does not promote people unless the department can justify a case of why a higher position is needed in that department. Often some people are left frustrated at the review process. Another downside is that you won't find typical corporate perks here like those sky box tickets to some professional sport or a huge Christmas gala. MITRE is a non-profit organization, and thus cannot provide these types of perks.