Acceptable Targets: Surprisingly, despite the majority of the enemies being Soviet soldiers (either past or alternate-present), most of the recordings and flashbacks do quite a bit to humanize the Russians in general. We see recordings of a couple deeply in love, leftovers of friends playing chess, teachers taking care of schoolchildren, and so on.
However, the evil masters of Katorga-12 were also intentionally exposing the children to E99 by putting it in their milk just to see the results, so while the people in general were human beings, the Soviet war machine was definitely run by evil bastards.
Complacent Gaming Syndrome: It's not hard to get through the entire game using only the Valkyrie assault rifle once you've gotten it early on, especially when you consider how quickly you can upgrade it. The plentiful ammo is also a point in its favor. In fact, despite the game giving you 7 normal weapons to choose from, there's really no reason to use anything other than the Valkyrie and the Volk shotgun; the Volk for blasting Zeks when they try to melee you, and the Valkyrie for everything else. Every other weapon in the game is simply too situational for general usage, with the exception of the Centurion revolver, which is just a plain useless joke weapon.
Well, no weapon except for the autocannon, which lacks iron sights and has a slight spin-up time, but also has range and accuracy comparable to the Valkyrie, while being able to spray out enough fire to chew through anything at close range as well, rendering both the Volk and Valkyrie largely redundant, as long as you have ammo... which will probably be all the time, because it carries so much of it, and is so powerful and accurate that most enemies can be taken out in short controlled bursts (yes, Singularity is a game where the minigun is a precision weapon!), with well enough to spare for the occasional panic spray against zeks. It's easy enough to get through the game with the Volk and Valkyrie: with the autocannon it's practically a joke.
Complete Monster: Dr. Nikolai Demichev is a former friend and partner of Dr. Barisov, the lead scientist of E99 experimentation on the island Katorga-12. Initially coming to power thanks to the E99 project, Demichev uses that power to divert resources to Katorga-12. In an alternate timeline where he survives a catastrophic accident on the island, Demichev authorizes unethical experiments on people of Katorga-12 against Barisov's orders. He soon demands Barisov hand over the newly developed TMD (Time Manipulation Device), and when Barisov refused he branded him and scientists loyal to him as "traitors" and ordered their execution. Unable to find the TMD, Demichev decided to direct his attention toward "Singularity", and after building a Singularity tower, Demichev started mass-producing E99 technology and weaponry, eventually convincing Premier Nikita Khrushchev to launch an attack on the West. Bringing the world to its knees with a single E99 bomb, causing horrific casualties, Demichev leads a successful coup against Khrushchev to seize control of the New World Government and declare himself Chancellor for life. Still keeping an eye on Katorga-12, Demichev authorizes horrible war crimes and executions as Captain Nate Renko tries to stop him. If Renko agrees to join him, Demichev will simply use him to destroy the Resistance before betraying him when he grows too popular with the people.
Demonic Spiders: The teleporting, phasing enemies which reoccur throughout the game are an absolute nightmare to fight. Even after you get the TMD, which allows you to knock them down for a fairly easy kill, the low amount of TMD energy and the high-cost to Impulse makes it a difficult tactic. They swarm you, in packs of three or more, and can kill you before you can even take one of them down.
And every time you think you've cleared the area, more teleport in.
Then there is that special mutant who appears a couple times who is immune to your deadlock power.
Foe Yay: In the final level, you can find early audio logs by Dr. Barisov and Dr. Demichev where they express the enormous admiration they have for each other. Although the two of them have a falling out when Barisov realizes Demichev is an amoral, power-mad loony, and Demichev realizes Barisov is not. Indeed, it seems Demichev made every effort to include Barisov in his plans for world domination, before finally getting tired of Barisov's Honor Before Reason and deciding to just kill the guy.
Goddamn Bats: Goddamn phase ticks! They usually appear in swarms and latch onto you and explode. Two of the TMD functions can save you from them (the Impulse wave, or the time-slowing Deadlock field) but they're still annoying, distracting, and potentially deadly if you're caught at an inopportune moment.
Narm: It seems very weird how a top-secret, isolated Soviet science project has a disproportionate number of written English mostly written in faux-Russian alphabet and also English-speaking domestic staff...
Paranoia Fuel: The first time you meet the "Echo" Zek, he jumps and takes a stab at you, after which he vanishes. If you have the Spikeshot rifle, you can use the thermal scope to look behind you... and see that he's still there. He stalks you for most of that chapter, and most people don't even know he's there.
The first half hour or so of the game plays out more like a Survival Horror game than a sci-fi shooter. Your helicopter goes down and you find yourself alone on a deserted island where it becomes increasingly obveious that something has seriously gone wrong here. You find only a pistol to defend yourself (along with the knife you start with) and start seeing ghostly flashbacks of what happened along with notes and messages left by the people who died there. Then you get jumped by something that looks like a cross between a zombie and the Slender Man, which you have to shoot off. Then you get to the school where things are even worse... At least its near here that you get some heavier firepower and meet up with your buddy Devlin.
Player Punch: Barisov's ending. As the details start slowly adding up, Devlin, who made himself fairly useful in fights, voiced the confusion the player was likely feeling in the early part of the game and was eventually murdered by Demichev, and is now alive and well, thanks to you, says, "Isn't that right, Comrade?" This moment tells you what's going on before the statue does, and it's your own buddy obliviously saying You Can't Go Home Again.
Special Effects Failure: The 3D modeler who made the Valkyrie had a bit of a brain fart; it has a folding stock, but the hinge is on the same side as the E99 tech sticking out. The stock wouldn't come close to resting flat against the rest of the gun and would stick out so much it would be more cumbersome than anything.
That One Level: "Escape the Sewers", which is where you first encounter the aforementioned Phase Ticks. The little buggers surround you very quickly and will eat up your health in no time. Meanwhile Renko has a bad tendency to perform actions like healing himself and refueling the TMD very slowly, during which you are unable to sprint as well, meaning you are at the mercy of the Phase Ticks until the action is complete (and because you don't actually heal until most of the "patching" animation is done, you can die whilst in the process of healing yourself). This combination of things, especially on Hard, makes this section a nightmare. Ultimately the best bet is to throw down a Deadlock in the center of the room, run into it, use the Impulse to blast any Phase Ticks that get caught in the bubble, then make a mad dash for the hallway and pray you have enough TMD energy to blast the remaining Ticks away as you encounter them until you reach the ladder at the end of the hallway, at which point you can breathe again.