Let me crystallize my thoughts on this:
The military runs rigorous physical training programs on many levels. This builds character, that much is clear. The intellectual part of personality development is, however, entirely missing in military training, if not actively discouraged - since there are no set answers here in western culture.
Certain internal martial arts institutions train very rigorously as well (you will get exactly the same character "benefits") but for a completely different purpose - to affect the mind.
People here keep on pointing out that the modern military is more effective in warfare but that is beside the point. If you have some irrational prejudice against eastern culture but want to become more of a person, i would personally opt for perhaps training with the military for a short time (move as high up as you can in physical training ranking) and then leave the army and join various urban military training programs whilst spending your spare time reading and thinking. Alot of you however are arguing against something you obviously dont understand which is fairly sad.
If, finally, you want to experience war, well that is something entirely different but you should know that you will spend most of your time playing video games in a camp and occasionally knocking civilian doors down to arrest and search people whilst running the risk of being sniped. All, again, for the fossil fuel CEOs.