Mass Effect & Mass Effect 2
The Alliance military is of great concern to the galaxy. At first contact with the turians, they were completely inexperienced. Turian disdain changed to respect after the relief of Shanxi, where the humans surprised them with novel techniques and tactics.
The human devotion to understanding and adapting to modern space warfare stunned the staid Council races. For hundreds of years, they had lived behind secure walls of long-proven technologies and tactics. The Council regards the Alliance as a 'sleeping giant'. Less than 3% of humans volunteer to serve in their military, a lower proportion than any other species.
While competent, Alliance soldiers are neither as professional as the turians nor as skilled as the asari. Their strengths lie in fire support, flexibility, and speed. They make up for lack of numbers with sophisticated technical support (VIs, drones, artillery, electronic warfare) and emphasis on mobility and individual initiative.
Their doctrine is not based on absorbing and dishing out heavy shocks like the turians and krogan. Rather, they bypass enemy strong points and launch seep into their rear, cutting supply lines and destroying headquarters and support units, leaving enemies to 'wither on the vine'.
On defense, the human military is a rapid reaction force that lives by Sun Tzu's maxim, 'He who tried to defend everything defends nothing.' Garrisons are intended for scouting rather than combat, avoiding engagement to observe and report on invaders using drones.
The token garrisons of human colonies make it easy for alien powers to secure them, for which the Alliance media criticizes the military. However, the powerful fleets stations at phase gate nexuses such as Arcturus are just a few hours or days from any colony within their sphere of responsibility. In the event of an attack, they respond with overwhelming force.