Singularity/YMMV

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 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.
Complete Monster: Demichev, to put it mildly.
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.
Nightmare Fuel: The Reverts and those sounds they make.
- If you look closely, you'll see that some Zeks are made out of 2 people fused together, probably the same person in 2 different timelines.
- You spend the entire game reverting tapes to hear messages. One of those tapes, for no apparent reason, suddenly causes a very short cutscene with a screaming corpse in your face. You'll hesitate to approach the next couple of tapes afterward.
- 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.
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.