This is an awesome game.If you like halo,doom,far cry and half-life you owe it to yourself to play this game.
It is graphically amazing and the gameplay is good as well.This game combines parts of doom,halo and half-life.Doom because of all the pop out of corner villains there are.Halo because of the epic battles with tons of enemies coming at you.Far cry because of the transformation you undergo when you have the mutegen.And Half-life because the whole story is told in your perspective wuth 1 or 2 cutscenes or cinematics.
During the story you become invloved in a three way between the good grey and the bad greys and the humans.
I don't want to spoil anything else so no more but it is an epic game that will take about 15-20 hours to beat.
The multiplayer is ok at best unless you consider infection which is a official zombies game where one person is infected.
This game in my oppinion is better than far cry,halo,doom and maybe half-life or tie.Though some might not agree it is still a good game that you should definetly buy or if nothing else rent.