Mercury isn't just your generic FPS. The player must tackle each mission with an attentive and vigilant nature as enemies may spot you before you spot them. 

The element of cover isn't common, utilize the environment and plan accordingly before making a move around enemies. 

Munitions are scarce, so do not go wasting your ammunition.

Enemies and weapons have certain ranges, you may be able to take out an enemy with precision from a distance without being seen by them whilst saving ammo.