Avantages
Learn new things Lateral move potential - each program/contract is very different Career trajectory is good Professional environment Great on a resume, great track record Stable, hard to get fired Good benefits, although they're getting squeezed over time like every over megacorp Very impressive 10% 401K match and $500(single)-$1k(married) HSA contribution Potential bonus for rock stars (manager's favorites) 9/80 schedule, every other Friday off Fair pay, negotiable w/ potential for relocation or sign-on bonuses. Overtime is paid and typically not mandatory, allowing good work/life balance.
Inconvénients
Large government contract = lots of red tape Outdated tools Sometimes poor workflow/poor attempt to adopt new methodologies like Agile You may be figuratively placed in a closet and forgotten for months Some work is mundane/monotonous bug-fixes or pure maintenance Difficult to use parental leave, FMLA, disability leave, or otherwise use your regular vacation time (program dependent) Laughable 0-4% raises