It's not just because he's a Nazi. It's because he's a smartass Nazi. As the main antagonist in Indiana Jones And The Great Circle, Emmerich Voss vacates the archetypal armchair usually reserved for secondary fascist goons, so that he can goosestep straight into the big boy seat himself. He smiles with all the sleaze of right-hand-man Major Toht, the grubby gestapo who gets that right hand burned in Raiders of the Lost Ark. Yet he also engages in the pseudo-intellectual trash talk of the main archaeological rivals to Jones, like Rene Belloq or Walter Donovan. He is a hideous grab bag of all the things that make an instantly detestable villain in the series. But there's something else. Voss is so immediately and gutturally hateable because he resembles a type of racist encountered not in the 1930s, but one you've probably met today: the asshole you meet on the internet.
Warning: Here be spoilers.
From the first moment we meet Voss in this pretty swell first-person adventure, he is unnerving. He touches his face in a weird way. He talks about the anatomy of the muscles around the mouth, observing that Vatican quisling Father Ventura has an interesting orbicularis orbis. This is already batshit villain behaviour and it evokes a kind of disgust at his creepiness. He's soon overpowering the "holy" man with blackmail and taking what he wants from the Vatican's vault of relics. Voss will continue in this vein throughout the game, alternating between slime and intimidation, but the nature of his blackmail is also the first sign of his other hobby: psychology.
This becomes clear when he's forced to work with Gantz, fellow Adolf stan and officer of the Wermacht. The two are at loggerheads, and Voss intentionally riles up his counterpart, telling an associate that this is all part of his method of control: "Nothing is quite so easy to manipulate as an insecure male". Gantz, for his part, is a hothead and a zealot for the Reich. He cannot see that Voss is simply saying whatever will most get him angry.
It is unclear if Voss even believes what he himself is saying half the time. Almost everything he says to other characters is unreliable, eel-like, the epitome of bad faith. Voss is not just a practitioner of psychology. He's a practitioner of dumbass pop psychology. He makes fun of Gantz' temper tantrums by doing an ape impression and ridiculing his "embarassing attempt at dominance". He's the kind of dude who keeps talking about the "alpha male" and "beta male" even when the source of that idea in animals has been largely disproved. He later comes to earn Gantz' unbending loyalty in a wild U-turn, mostly by accidently saving the man's life, but he grabs hold of that not with the instincts of a wolf, but with the slathering opportunism of a hyena.
So, Voss is psychologically manipulative. This is run-of-the-mill villainous behaviour, but nothing new in the grand scheme of things, true. Yet it is the quality and style of his manipulation that makes him so recognisably repugnant. He is a shit-stirrer transparently. He doesn't attempt to hide what he is doing, and laughs as he goes about it. While Indy and Gina have him kneeling at gunpoint, he chuckles as he needles Jones about his past relationships. "Were you afraid of becoming a father?" he asks, then, with that sleazeball smile. "No, you were afraid of becoming your father."
There is absolutely no half-throttle with this guy, he just goes straight for whatever will make you uneasy. He's not Walter White, he manipulates emotions in the same way an internet troll does. Openly, in plain sight, with a shit-eating grin. There is, I suspect, a reason his face has all the folds and wrinkles of a famous meme. He is constantly smiling at the annoyance, anger, and anxiety he induces. What a fantastic shitheel.
He also has an answer for everything. Or rather, an annoying question for everything. When Indy is trying to decipher a lost language in the Nazi's presence, Voss sneers at his every conjecture, fusses over every observation - all an attempt to infuriate Indy and get him to reveal his knowledge in an act of impatience. In doing this, Voss reminds me of another internet archetype - Mr Gotcha - the deeply irritating whataboutist who seems to intentionally miss the point of any valid criticism by making some unrelated counterpoint. "We should improve archaeology somewhat," you might say to Voss. "And yet you participate in archaeology, Dr Jones. Interesting." Oh, fuck OFF, Emmerich.
Voss is a powerful figure in the story - and the best written character in it, for my money - because he morphs a classic figure of hate into a form we can easily recognise today. The Nazis of the mid-twentieth century grow more distant as the decades pass, and in becoming the endlessly killable bogeymen of video games they are turned into a kind of warning myth that we can shoot, but never see close-up. Like a marble statue of antiquity, we know what that hate looked like in form, but we don't see the colour it was once painted. Voss lets us encounter a fascist in full colour, even if the saturation is sometimes pumped up to exaggerated levels. He sees everything through an immature lens of power and takes pleasure not just in having power over others, like any baddie, but in annoying and humiliating them on top of that. He is an awful schoolboy bully who learned some big words.
When the game starts up, you'll see a disclaimer message explicitly saying the game doesn't endorse nazism. This is a legal thing, probably, but also a comically unnecessary warning. It's doubly unnecessary to anyone who meets Voss. A man so ferociously disquieting that finding out how he is going to die is just as powerful a motivator toward finishing the game as finding the next vivid explorable location. The developers at Machine Games suggested in a behind-the-scenes marketing video that they intended for him to get under the player's skin in the same way as he gets under Indy's skin. Well, mission accomplished. I am simultaneously glad to have encountered him and foaming at the mouth with rage any time I think of him. Which, in hindsight, is a splintered state of mind he would absolutely love to see, the astounding rat fucker.