Pros
Certainly there are (very) smart individuals interspersed throughout the employee population. Several governmental programs (typically DC- or site-local) are quite relevant, challenging, and central to the public interest. Benefits, retirement-matching, and vacation packages, though recently reduced, are still generous relative to industry. Work-life balance differs from job to job, but seems to be 'good' across the board, often to the point of 'cushy' or 'overly lax.' MITRE's anomalous retention (15-to-35 yrs) and attrition (frequently 2%, and never higher than ~6%) could be seen as either pros or cons, but generally seem 'beneficial' in that, once in, employees want to stay. Working mothers are gently (cushily) treated by the corporation, as are the aging and infirm.
Cons
Years and years ago -- nearly back to its inception -- MITRE (re)defined its FFRDC role so as to focus on "attaboys" (customer approval, published praise), rather than traditional profit/loss or similar competitive measure(s). While clever (in that it dodges traditional metrics and accountability), this 'flavor' has leeched into all nooks and crannies of corporate culture, such that most internal decisions (personnel management, promotion of staff, research-program grants, valuations of individual work-programs/departments, yearly performance reviews) are subjective nearly to the point of lacking substance. The resultant office 'vibe' is very feudal (individual fiefdoms and turf-wars competing for (relatively) small stakes), and academic-graybeard (employees stay for life, and have motivations/priorities unlike that of outside industry, and move/act sloooowly), and somewhat out-of-touch (no, sir, we don't do the actual work, we advise you on _how_ it should be done). MITRE's aforementioned focus on the (intangible) "attaboy, you did a good job" has spawned many downstream consequences. Cronyism exists, due to the tenured-professor politicking referenced above, but also because, in many cases, mid/senior leadership can no longer differentiate a "good performer" from an "average [or lackluster] performer," thus those who cling closest to the boss(es) frequently receive the choicest assignments or promotions. Ambitious players are learning that, since no consistent quantitative measure of 'how much improvement' or 'how much technical quality' exists within the organization, it is possible (preferable?) to hop from project to project, dipping one's toe into each work-effort (or, worse, stealing credit) just enough to appear competent and milk customer-satisfaction, before moving on to the next stepping-stone -- in essence, salesmanship and business-development behaviors, emerging within a supposedly-not-profit-driven culture, and being disproportionately rewarded in comparison to 'traditional tech' or 'traditional management.' This cultural erosion has not gone unnoticed by outside industry. Cheaper for-profit competitors are beginning to poke at the FFRDC niche, even pointing out areas where the company "is doing [staff augmentation] work it's not supposed to do." Further, a generational void is manifesting within MITRE's ranks... young college/twenty-something hires are "still learning" (picking up early-career skills), while longtime veterans are plodding through the daily routine (and/or "just hoping they can make it another few years"), but the hot-to-advance prime-of-life Generation Xers are exiting in droves, or, tragically, never joining up in the first place. Worst of all, many MITRE-ites find themselves unemployable (due to lack of current skills and/or recent hands-on experience) when returning to the outside job market.