Half-Life has an ecology and a society. Monsters are breeding, herds are forming, and some monsters prey on others. Players are dropped into the middle of this environment and must learn from what they see. In order to survive, they must use both their weapons and their wits. For instance, an underground train system takes players to numerous stations and allows them to backtrack.
Some vehicles also contain, or can be used as, weapons to mow down monsters.
Ducking, crouching, and crawling For more realistic and varied action, Half-Life lets players duck and crawl in addition to stand, walk, run, and jump. In addition to expanding players' tactical options, being able to duck and crawl opens up myriad spaces once sealed off to first-person shooters, such as a maze of duct work which can be used to help elude monsters or reach otherwise impossible rooms. In Half-Life, physics and gravity behave more like in the real world than in other. Flooring can be unstable and rickety railings can give way. Even typical tactics for obliterating the enemy must yield to Newtonian physics.