"Shoot mercilessly with this third-person shooter game"
Gears of War brought third-person shooters into fashion by implementing a shooting mechanics as precise as it is spectacular. This sub-genre does not usually receive high quality pitches, but from time to time a few games of the stature of Overkill 3 arise.
In this case there is no line of argument and the movement of the protagonist, except on rare occasions, is not controllable by you. Everything is based on annihilating your enemies by shooting them with a multitude of weapons, having to aim precisely at their vital areas to end their lives and continue advancing through the various scenarios.
The Overkill 3 phases propose secondary missions that must be completed in order to have access to the rest of the levels. They'll also give you money to buy weapons, ammunition, grenades, medical kits and other useful items.