Most interestingly, there is a gameplay structure central to the game based on the Predators' insistence on honour. The worthy kills you make as you progress contribute towards rewarding you with new upgrades and weapons, while killing unarmed humans seriously diminishes your honour rating.
Happily, human grunts with machine guns are fair game, while defending the innocent from Aliens will boost your rating immensely. There is also an energy bar than runs alongside the typical regenerative health bar. This secondary bar can be depleted to replace health or to permit the use of more powerful weapons, allowing for a small amount of on the fly strategy and decision making as you choose between your own well-being and destructive power.