Over the years there has been many shooter games that have had people take down aliens, zombies or even demons from hell and throughout this list you will find some of the most greatest shooters of all time.
1. borderlands 1-3
in borderlands you play as vault hunters in a planet that has been broken down into a sort of junkyard. the main goal that all the villains try to achieve is to open a vault that has been allegedly hidden on the planet and has all sorts of riches and power inside it.
in borderlands you fight bandits, alien like creatures and even robots and as you do you also collect guns and the interesting thing is that no gun is the same and each has random stats.
left for dead is a zombie shooter game where you can choose between 4 characters (although this has no effect on the game) and with weapons you find in the levels you can chop, explode and gun down the zombies. in left for dead there are differant types of zombies that might explode or jump at you so as to not keep each level the same. each set of levels is cut into chapters where you try to get past a certain place wether that be a mall or carnival.
WWz is alot like left for dead except you have a multitude of classes to choose from like a trapper or a gunner that can help you fight the zombies as you play through the differant levels
4. the metro series
the metro series is a shooter game with an amazing story about a wasteland that people have survived in after a nuclear bomb has gone off above, these people have survived due to them staying down in the metro tunnels, where alot of the action takes place. you will either fight other human bandits or you will fight mutant rats or dogs. ammo is a bit scarce in this game so players are forced to scavenge or simply play it stealthier as to not use so much ammo.
doom is a gory, fun game about slaughtering demons with lots of blood and guts. it is very fast paced and you have a multitude of guns at your disposal which, when you run out of ammo, can switch to.