Pros
MITRE has an excellent reputation in the federal gvernment. The name itself brings in new opportunities, and is good for your resume. MITRE is rebranding itself as a systems engineering resource for the governemnt. A good thing because this skill is in high demand. You don't need to be an engineer, but you wil lfit in if you are a systematic and collaborative technical thinker with altruistic and academic leanings. There are many opportunities for diverse assignments if you seek them out. "Work-Life balance" is not just a HR slogan but a true MITRE value. There are plenty of workaholics but they are doing what they enjoy. No one is forced to slave away at proposals on the weekend or market new business opportunities. You can really serve as an honest broker to the government. A good place for mid/late-career techie professionals wanting to help the government.
Cons
Promotions and lateral transfers are difficult. Management tends to be comprised of introverted technical types who have few management or people skills. The company is becoming top-heavy with integration directors and thought leaders who have lost touch with what is going on at the operational level. Site employees, even those with high clearances, are getting overlooked. Not a good place to work if you are a MBA graduate, ambitious, or entrepreneurial.