Outstanding career, lots of opportunities
Pros
Fascinating work, frequent opportunities for training, good pay, transparent evaluation and pay system, regular raises, predictable promotions. Frequent opportunities for travel. Many amazing duty stations. Intelligent and motivated peers. Usually good leadership.
Cons
When you join the military, you lose a level of autonomy. You have to deploy for periods of 4-12 months at various points throughout your career. Frequent moves make it hard for a spouse or partner to maintain their own careers. Some of duty stations are mediocre. You have to be willing to risk your life if ordered to do so. It is becoming politically and morally more complex to serve in the military. Finally, the work-life balance is often not good, though this depends on the specific job. Sometimes it involves shift work (12 hour shifts), sometimes just long hours.