Pros
The best reasons to establish a career in the US Army are: 1. To serve and protect the United States and its Constitution from enemies and threats, which provides a sense of fulfillment found in very few other careers. 2. To receive some of the best pay, entitlements, and retirement benefits available in the entire country. 3. To serve in a very diverse organization in which there still exists a sense of community and camaraderie that is deep, long-lasting, fulfilling, and unique.
Cons
The top reasons to discontinue a career in the Army are: 1. Bureaucracy: the US military is the largest bureaucracy in the entire country. Hundreds of thousands of regulations, operating procedures, rules, and guidance make for order and discipline but also for an organization that is too often not only slow to change, but resistant to it. The bureaucratic nature of the organization also places policies ahead of people, often turning Service Members into mere numbers in a huge system. 2. Socialism. Despite the fact that most Service Members are rather conservative (at least in regards to financial policy), they benefit from one of the most socialist systems in the entire U.S. That is, everyone is essentially rewarded the same often regardless of work, effort, or outcome. A Service Member who works him/herself to the bone is just as likely to be promoted as the one who did the minimum. In the military there exists little incentive to excel beyond one's personal drive to do so (if it exists). This is apparent especially to officers; many of the best abandon the Army early in their careers -- forced to wait their turn or their time despite their demonstrated performance. This leads to a glut of lower-performing or self-interested leaders and officers swelling the upper-ranks. 3. Lack of Challenge: For Officers, one eventually reaches the point in an Army career -- as a senior captain or a major -- where one primarily only conducts staff work (essentially planning focused on operations and logistics in an office environment). One may change units or go to a new station or office and yet the work largely remains the same -- any challenge (and ensuing growth) -- is short-lived. It becomes mundane, boring, and pat.