* AlternativeCharacterInterpretation: [[spoiler: Mrs. Waite and why she [[OffingTheOffspring killed Ramona]]. Did she really kill her because she had become a wild and ferocious beast, or was there an actual reason behind it? It's possible she read her husband Thomas's diary (which was in the attic with her) and discovered that Thomas was disgusted by their marriage and was considering giving their HalfHumanHybrid daughter a MercyKill before she became a full Deep One herself. Mrs. Waite could've then killed Ramona to either spite her husband, or as an attempt to make him happy by relieving him of having to kill their daughter himself.]]
* AnticlimaxBoss: [[spoiler:Mother Hydra. She has no way of actually attacking you, her only defense is a bunch of respawning Deep Ones, but they are absolutely no problem when the Yithian Lightning Gun can kill them in one hit and has infinite ammo.]]
* BestLevelEver: One of the most praised levels in the game is the [[spoiler: hotel escape, where you have to flee an entire town of cultists. You have no weapons, no allies, no mission... all you can do is run, bolting doors behind you while desperately trying to find a way out.]]
** On the same token, the cutter level. [[spoiler:To go into further detail: Jack has been fished out of the water by a Coast Guard Cutter (a ship operated by the coast guard that is at least over 65 feet long), when suddenly it comes under attack by the Deep Ones, who pour onto the deck and start killing everything. The crew arm themselves with Springfield rifles and Tommy guns, eventually fighting off the Deep One assault... [[OhCrap then Father Dagon shows up]]. With almost everyone else on the ship dead, Jack singlehandedly takes down Dagon with the main gun by firing missiles into his face before Dagon manages to sink the boat.]] Unless you get the GameBreakingBug in which the ship doesn't get close enough to shore for you to target correctly, resulting in a game that can't progress until you get the fan-made patch.
* BreatherLevel: The surface of the Devil's Reef. The level is quite short, devoid of enemies, and miss sanity-damaging stuff.
* CommonKnowledge: Everyone knows this game is an adaptation of ''Literature/TheShadowOverInnsmouth''. Except it's not. It's actually an adaptation of the "Escape from Innsmouth" campaign from ''TabletopGame/CallOfCthulhu''. However, since the original story is much more famous and the campaign is now obscure due to being out of print, not many people realize this.
* CompleteMonster: [[HumansAreTheRealMonsters Robert Marsh]] is the main mortal antagonist of the game. The heir of the Marsh family who sold Innsmouth out to the gods of the [[EldritchAbomination Deep Ones]], Robert and his elder brother Sebastian rule over [[ReligionOfEvil the Esoteric Order of Dagon]]. While Sebastian focuses on the business aspects, Robert is a religious fanatic who presides over a legacy of HumanSacrifice and fanaticism. When ordering [[PlayerCharacter Boston police detective Jack Walters]] killed in [[Literature/TheShadowOverInnsmouth Innsmouth]], Robert later uses his magic to help kill the marines who attempt to storm the Order before summoning Father Dagon himself to lead a horde of Deep Ones to a marine vessel that results in the deaths of everyone but Jack. When Y'ha-nthlei, the Deep Ones' city, is attacked, Sebastian furiously confronts Robert over having the Order in religious devotion in a time of crisis and attempts to shoot him, resulting in Robert magically [[CainAndAbel murdering his brother]]. His ultimate goal is to have the Deep Ones [[OmnicidalManiac overwhelm all of humanity]], declaring the time of the human race is finished. Having nearly fully transitioned into a monstrous Deep One, Robert cares only for his bloodthirsty religion, with even the other citizens of Innsmouth fearing him.
* ContinuityLockout: Those unfamiliar with Lovecraft's work will probably find the reveal that [[spoiler:Jack is part Yith and has the body-swapping ability to go with it]] somewhat confusing.
* DisappointingLastLevel: A pretty serious case too. It's quite clear that most of the game's development went into the first half of the game. The last two levels are particularly problematic.
* FridgeBrilliance: Jack's ability to [[spoiler: take over the body of a Deep One]] seems out-of-context at first, since up to that point his PsychicPowers only went as far as a few random visions. However, it makes a ''lot'' more sense when you realize that [[spoiler: it's an inherited Yithian trait, the ability to swap bodies across space and time]].
* HesJustHiding: Some fans believe that [[spoiler:Jack]] didn't really die at the end, and instead [[spoiler:secretly swapped bodies with someone else, and is now carrying out his mission to dispose of the remaining Flying Polyps, [[GrandTheftMe using another person's body]] to accomplish this task]].
* HilariousInHindsight: ''Dark Corners of the Earth'' has you battle a ReligionOfEvil that plans to take over the world in the name of a deity named Dagon. Guess what happens in [[VideoGame/TheElderScrollsIVOblivion the next game]] that Bethesda released? There's even a side-quest in that game that's a direct homage to ''Literature/TheShadowOverInnsmouth'', the story that ''Dark Corners'' is based on.
** Four years after ''Dark Corners of the Earth'''s release, publisher Bethesda would acquire [[Creator/IdSoftware a company]] known for developing [[VideoGame/QuakeI another Lovecraft-inspired]] FirstPersonShooter.
** The nightmares/hallucinations that Jack has about Arkham Asylum can be considered the larval form of ''VideoGame/TheEvilWithin'', which Bethesda later published and also had psychological horror as a central theme.
* MemeticMutation: Thanks to Podcast/FourPlayerPodcast, Elliott Ropes, the guard in the general store has gained the FanNickname "Giant Spook Man".
* SugarWiki/MomentOfAwesome: By the end of the game, Jack has done several awesome things within the week. Namely, he fought his way out of Innsmouth, killed a number of cultists, [[spoiler:destroyed a shoggoth with factory machinery, blew up Dagon by blasting him in the face, vanquished the cult leader Robert Marsh armed only with a knife, took on two Flying Polyps on very unforgiving terrain, dismantled the Esoteric Order of Dagon and electrocuted Hydra.]] All without going completely insane. [[spoiler:Until the ending, that is.]]
* {{Narm}}: The slow motion effect that kicks in upon a GameOver also slows down dialogue. This is mainly noticeable on the rare NonstandardGameOver where Jack is still alive to say something, like failing to save [[spoiler:Hoover]].
--> Jack: Noooooooo, I'm toooooo laaaaaaaate.
* NightmareFuel: [[NightmareFuel/CallOfCthulhuDarkCornersOfTheEarth Has its own page.]]
* PortingDisaster:
** The speed of every character is decreased in the PC version compared to the Xbox version. It makes the game nearly unwinnable when [[spoiler:the last level ends with a desperate run toward a gate while the ceiling is collapsing]]. The Steam version lacks this glitch, though the time limit is so tight it is hard to notice.
** The Steam version has its own issues, though, as it's infamous for crashing a lot, to the point where reviews of the game on Steam are very mixed.
* SpiritualSuccessor: Seems to owe much more to the original ''[[VideoGame/QuakeI Quake]]'' than ''VideoGame/QuakeII'', ''VideoGame/QuakeIIIArena'', and ''VideoGame/QuakeIV'' ever did. The only thing missing is a multiplayer mode.
* {{Squick}}: Mother Hydra. She has scales, is grotesquely fat, has razor sharp teeth, and has [[MultiBoobage four giant breasts]]. She's just... ''gross''.
* ThatOneBoss: [[spoiler:The pair of Flying Polyps. Though they don't do a lot of damage to you when the attack, the terrain they are on is narrow enough to fall off if you walk carelessly. Add in that their method of attacking involves pushing you our pulling you towards them with powerful winds makes this even harder.]]
** [[spoiler:In addition, you have to fully charge your Yithian weapon (which is the only thing that can hurt them) and fire at them. Oh, and they can teleport.]]
* ThatOneLevel:
** The Marsh Refinery. You do get plenty of ammo and weapons, but the game more than makes up for that generosity by making it easy to take a wrong turn and completely miss the key item you'll eventually need to progress, lengthy areas on catwalks and platforms where enemies can snipe at you from above ''and'' below, and even a couple of spots where the enemies will ''respawn'', unlike most other areas in the game. Also, ever hear tale of a [[PuzzleBoss shoggoth?]]
** The penultimate level in the Deep One's underground city is absolutely ''infuriating'' in just how annoying it is. Mostly because it has one of the most insane, long, and GuideDangIt puzzles in the history of video games that requires a bunch of backtracking and searching.