Ammo-Using Melee Weapon: The Chainsaw requires rare fuel to offset its immense power.He also sincerely thanks VEGA before its sacrifice and meltdown. Partly because killing him would be rude, and partly because he's not sure if he can kill him. Even after turning on Doomguy, he admits Doomguy might be right to completely obliterate Hell, and merely sends Doomguy to parts unknown to keep him from interfering. Affably Evil: Well-Intentioned Extremist Samuel Hayden, who is unfailingly polite to the Doomguy and assists him throughout despite their at odds agendas - even after Doomguy repeatedly thrashes the UAC facility against his protests, he continues to assist him, and never has anything worse to say than some passive-aggressive comments on Doomguy's preference for violence.Most of this is due to Olivia Pierce turning the UAC Division on Mars into her own cult, but Samuel Hayden essentially let her do whatever she wanted, as long as he got results (i.e.: working Argent energy). Oh, and they don't let their employees take the weekends off. In this Doom, the UAC operate like a cult and are essentially a combination of Satanism and Unitology, getting there by way of Weyland-Yutani, but Played for Laughs (most of the time) while operating with a hilariously cavalier attitude towards the deaths of their employees. Adaptational Villainy: In Doom 3, the UAC were somewhat amoral, but were surprisingly sensible and generally averted the stupidity of most evil corporations like Umbrella.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.