Bad Mojo, an old DOS adventure game from the mid ninenties. In this game, you're a freaking cockroach and, as predictable, you get to witness all sort of weird and disturbing things, such as a dead rat, shown in all its nauseatingly glory.
Protozoid Slimers from Duke Nukem 3D are toothy piles of boneless slush that leap from ceilings and crawl onto you face, providing you with plenty of Interface Screw in the process, until you kick them off.
The Freak Show level of Carn Evil. If the Bearded Lady's corpse doesn't make you sick, the worms with human faces that come out of her body, and the gimp-grinding machines, will.
Dead Space, There are several sections of the game that involve running around solving puzzles and fighting creatures in zero gravity. You're able to jump around and stick to surfaces, so what was the ceiling a minute ago may become the floor. Especially pukeworthy if you have to fight while doing it.
Not to mention the fact that the game contains enough severed body parts to choke a whale.
Even Isaac seems to think Meat Moss sections are disgusting; not only can you not run over the ick-covered floors, but he adopts a new walking animation where he appears to be moving gingerly and trying not to come into contact with any of it. That these segments also have corpses fused into the walls - some of them still moving - does not help.
The appropriately-named Pukers from Dead Space 2, they who projectile-vomit acid onto you, the same acid which is causing their bodies to visibly break down, are especially disgusting, even among the horrific menagerie of the Necromorphs. It has been said by Visceral Games that the sound designer who was recording their audio was attempting to make himself dry heave through a method he obtained on the Internet, only to do it wrong and actually make himself vomit - and because the microphone was on, it captured that in all its messy glory and the sound team decided to actually use that sound in the game. Oh, and it's grapple attack is to rip Isaac's helmet off and vomit into his mouth.
Halo: Combat Evolved: 343 Guilty Spark! Some people may feel sick after plowing for a lengthy time through twisted and mutated both enemies and comrades, some of them spontaneously exploding with wet balloon-like bangs and everybody leaving yellowish-brown "blood" stains everywhere... it doesn't help much that if you don't pay attention, you can easily get lost in that large complex with said mutations constantly respawning...
All the monsters are purposefully designed to be as nauseating as possible. The third game once again provides the best examples, including but not limited to hulking, vaguely humanoid bloated masses of flesh (appropriately named "insane cancers"), a massive, grotesquely phallic worm, and horribly burnt, loosely-bandaged dogs with their heads split in half.
The Abstract Daddy/Doorman monsters in the second game really deserve a mention. Their appearance is disgusting enough, but as for what they represent...no, just no.
In the same vein, Haunting Ground has a similarly gut-wrenching death where Daniella is heard ripping out Fiona's uterus and moaning loudly, having stolen her Azoth.
Some of the Cobra Unit fall to this trope, especially the Pain who is covered in bees and has his face swollen from all the stings, as well as the Fear who is a human spider capable of twisting his body in unnatural ways and a tongue to rival Orochimaru's. Eww... And The End, whose eyeballs bulge out a lot.
In the Grand Theft Auto: Vice City mission "Boomshine Saigon," Tommy has to take Phil Cassidy to the hospital after he blows off his arm. The risk of nausea comes from trying to drive him to the hospital through the Woosy-cam where the screen appears to rock from side to side. If you suffer from motion-sickness, this might induce it. See it here.
Grand Theft Auto IV also has the camera get blurry and shaky every time you decide to get drunk with a friend, making especially driving a cause for motion sickness. It is amusing however to see Roman walk into a pole and fall over.
With stumbling into rooms to find them covered in blood. Or walking into a room you just tossed a proximity mine into, only to find the floor coated in blood and the remains of one of the two soldiers killed by it — a pair of feet and shins, and an arm.
Or toppling cover onto a corpse, only to have it twitch spasmodically as if it were still alive and in pain. At least, after you stop laughing at it.
Saya no Uta — Play this and try not to get ill at least once. Trust me, unless you have the morals of Hannibal Lecter, it's hard.
The Bee Bee Gun power in Bioshock is both frightening and downright disgusting. You can actually see the flesh on your arm covered with inflamed lumps full of bee eggs, while bees crawl around on your twitching hand... nasty.
"Remember, blood's the best lubricant!" And anything else the Creeper has to say.
The swarm of rats that comes pouring out of a Fester's torn-open stomach.
Parasite Eve is full of this. A rat's skin peeling apart and hanging from its body in bloody strips? Check. A woman's mouth splitting at the corners and stretching her face into a toothy rictus? Check. And that's just the beginning.
The second game even manages a sort of Nausea Fuel Discretion Shot in the animal testing lab. Nothing's shown on-screen, but examining a monkey in a cage brings up a message informing the player that it's eating its own fingers.
Doom for Xbox. It didn't get much right, but they did do well on the gore. In one player-activated scene, a corpse is drawn up into the air conditioning vent, and then highly detailed chunks of it fall back out. Most of the corpse wetly slams back into the floor. Apparently that's Cookie Monster up there.
The Forgotten Depths subzone of the Throne of Thunder. Specifically, the corpse-ridden sewer system beneath Ji-Kun's roost, riddled with such delightfully-named enemies as Bore Worm, Corpse Spider and Bow Fly Swarm that inhabit the fly-infested ribcages and murky waters you have to wade through. This isn't the first time World of Warcraft has featured bloody and/or rotten corpses lying around, but before this they didn't really show what kind of horrors tend to migrate to such things...
The Gluttony punishments in Afterlife all revolve around making the damned eat things they aren't supposed to. Special mention goes to "The Bowels of Hell," in which the damned are a) sewn to the inside of the intestines of a giant archdemon who has been eating nothing but Mexican food and b) have a plastic feeding tube crammed down their throats, which is connected to the "other end" of the digestive tract of the SOUL next to him. It makes its own in-game description throw up.
Left 4 Dead: Have you ever tried to listen to all the sounds the Boomer makes? It really begins to make you feel kind of sick, yourself.
Phantasmagoria has its fair share of outright disgusting scenes. The all-time winner, however, has to be Regina's death. She's locked into a chair, while a massive funnel is forced into her mouth. Carno then walks in, carrying a massive plate of sauce-covered entrails, brains, and other assorted guts. He then proceeds to force feed them down her throat, pausing occasionally to ram a pole down the funnel to make sure everything's going through all the way. When she finally dies, either the sauce or her blood is oozing out from the funnel's sides.
The bit on the S.S. Anne in Red and Blue versions where the player character (10 YEARS OLD) gives the captain of the S.S. Anne a back rub. It gets even worse in the ROM hackPokémon Quartz where you meet said captain and he brags about it like a pedophile.
Cubivore features you as a cube who goes around tearing off meat flaps from other cube in order to add said meat flaps to your own being. How is a cube able to do all that? Well it's All There in the Manual your cube is full of organs including a digestive tract and a stomach. Just Squick.
In Amnesia: The Dark Descent, when your sanity starts to go down when you're in the dark, the screen gets all wibbly-wobbley and you hear a strange gravelly noise. The sound you are hearing is protagonist grinding his teeth together.
A minor one from Super Mario Sunshine: The eel in Noki Bay. The pollution is caused from his cavities. Let that sink in for a second. The pollution is actually globs of saliva (and whatever else was in his mouth) laden with cavity-causing bacteria to the point of becoming HIGHLY TOXIC. And you had to swim through that spit to get down to him, didn't you?
In Maniac Mansion one of the ways you die is to play the Tentacle Mating song with Green Tentacle in the room. Just think about that.
Marimo's death CG in Muv-Luv Alternative is especially gruesome. The BETA themselves are fairly nauseating.
The barnacles in Half-Life 2 have been graphically upgraded so that they're slimier and grosser.
Yoshi's Island is a cute, heartwarming game all the way through, except for the boss battle where you are eaten by the frog and have to kill it from the inside. The part inside the frog isn't the gross part. Not even close. The gross part comes after you defeat it, Yoshi goes down the intestine and then comes out the other end, and looks completely disgusted while the frog is lying there dead.
LIMBO gives us [[pulling off a giant spider leg with visible veins attatched and having to roll the husk over spikes]]. With sound effects! Ughh. Even those who aren't arachnophobic or bothered by gore will at least cringe a bit.
While not disgusting, Mirror's Edge can be this because the camera perfectly follows the protagonist's eyes and when she rolls, so does the camera.
Likewise Descent can cause this problem as well because of the six degrees of movement that the player has.
Top Banana's backgrounds resemble a random arrangement of 16x16 pixel tiles from some digitized painting of a rainforest. The Acorn Archimedes version is less pixelated than the more widely distributed Amiga version, but still not much easier on the eyes.
Ark Area, an Arcade Game by UPL, abuses a feature of UPL's later 8-bit hardware in Area 16 and Area 23 to make every single player, enemy and bonus sprite leave artifacts all over the screen, with the palette constantly flickering on top of that.