Actionized Sequel: While Doom 3 was more of a survival-horror, this entry is a straight-up action game in the vein of the first two.Possessed engineers don't blow themselves up on purpose, but they're melee enemies with a volatile gas tank fused into their torso, so the result is basically the same if you let them get too close and then shoot them without realising what exactly you're doing there.Lost Souls fly straight towards you, kamikaze-style.Absurdly High Level Cap: In multiplayer, there are 600 total levels the player can advance through, with 50 levels scattered across 12 epsilons.It's also a neat explanation as to why the little thing has infinite ammo. Abnormal Ammo: Most guns avert this despite incorporating Argent power technology one way or another, but the pistol makes up for it by directly converting Argent energy into gel bullets that behave more or less like 'real' slugs.The game keeps track of most categories through various achievements. And once you've bagged all of those, chances are you still have to complete some of up to two mastery challenges per weapon. 100% Completion: Most levels have three bonus objectives to complete, a combat rating that goes up by killing enemies, and numerous collectibles, mods, and secrets to find.