These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Contested Sequel: With regards to the Typing spin-offs, Overkill. While it's still the same B-movie hilarity as its original counterpart, only with typing instead of shooting, they lack the unique boss gimmicks of previous games — most of them are just a continuation of the "type stuff to damage them" premise rather than posing unique challenges.
Demonic Spiders: There's bound to be at least one or two per game. The Hermit and The Lovers are literal examples (though they're bosses, so they don't really count). Also notable is the Puker from Overkill, which can often damage you no matter how quickly you shoot them.
More specifically, if they are killed by anything other than a head-shot, they explode. If they are too close to you when they do so, you will take heavy damage. Ironically, if you let them grab you, it's easier to shake them off before they damage you — which is fatal to them without doing anything to you. The problem is shaking them off while other mutants move in...
The last boss spawns them, and they break your view — you can't shake them off, and you have to give them about five seconds of sustained fire to make sure they're dead for sure. Most of the time, they'll be stunned, then resume barreling towards you.
The riot shield-equipped mutants to some extent.
Taken Up to Eleven on the PS3 exclusive Hardcore Mode where you're required to kill only with headshots. It's not that bad, until you face these guys where not only do you need to get rid of their shield, you still need to take out their helmets. And you've also got a swarm of other zombies getting pot shots on you.
Goddamned Bats: Every. Single. Game. In addition, HOTD 2 manages to add the even-more-annoying kamikaze zombie owls alongside energetic, knife-handed midgets.
Overkill adds in exploding zombies mutants, that, if you don't nail with a headshot, will damage you immediately. The last boss spawns them endlessly.
Hilarious in Hindsight: Play the game normally till you reach "Carny" and Washington will say something to Varla about him and Agent Gwendolyn that they are going to check out the place. In the PS3 version, after clearing "Classic Mode" (you can only use the default gun and nothing else), you get the Gwendolyn gun; Isaac's favorite guns.
Memetic Mutation: Sega and Namco shooter translations seem to feature a running joke of having hostages shout "Don't come!" They've been doing it for years, bless them.
The infamous "Suffer like G did?" line in HOTD 2. It would have been imposing if the creature hadn't presented it as a question.
The grunts and groans when a character is injured ("AGH!") also count.
Narm: "The original sin that man is resphaansible to... To protect the loyfe coycle! I have maaaig a creacher to rule over maaahn kiiine! This is tha faynl bawdl! Shoe yourself! Our new ruler, the Empurr!" *followed by the camera pointing at a wall*
In fact, anything anyone says in House of the Dead 2 (and there's plenty of examples in the other games as well). There's enough to fill their own page. How could anyone do that?
Squick: Fat zombies that can have holes punched in them, incest in Overkill, open beating hearts... there's frequently stuff one shouldn't dwell upon. Some of the water zombies in House of the Dead 2 look like they could be Tarman's clone, and Tarman is rather Squicky to a lot of people.
Then there's more of Overkill, where we have macabre, disgusting bosses like the freaks in the Carnival, the Lobber, and Mother itself. It doesn't help that when she spawns mooks from her... erhm... womb, it looks like she's defecating. Also Warden Darling kissing his old, withered mother on the lips and Varla after her operation, with Mother's brain sticking out of her head. After the final boss fight, Darling also tries to atone by returning to the womb. Literally.
Surprisingly Improved Sequel: While all of the games in the series are generally good, III is notable in that the voice-acting took a serious level in competence. By 4, it's easy to forget the earlier games' Narmy goodness.
That One Attack: Ask anyone who has endured through The Fool's final attacks.
One of The Star's attacks is basically a Beam Spam attack, shooting six to eighteen energy blades at you. Playing 2-player mode? Get ready see up to 'twenty-four' of the bloody fucking things on the screen AT ONCE. Oh, and his Tornado Spin too. Pray your gun's sensors doesn't fuck up.
What an Idiot: In House of the 4, during the ending The World has been beaten, it mutates even more, followed by James activating a bomb in his PDA powerful enough destroy it. You'd Expect:For James to chuck that thing like no tomorrow, destroying The World so he and Kate can continue fighting the zombie apocalypse together. Even Max would have done the same if he was in James' shoes. Instead:James performs a Heroic Sacrifice by diving right into The World with his PDA time bomb in hand, taking The World with him.
Special Effect Failure: Some shots of the protagonists shooting at zombies in the first film were from the original game, with an "Insert Coin" message blinking on the screen!
They Just Didn't Care: Nowhere does it become more apparent than in the "Funny Version" of the first film, where we see endless scenes of everyone involved in the production screwing around.
With a plot involving teenagers going to a rave, in-game footage used as part of the movie, and only a brief cameo of the games' characters at the end, let's just say that movie never existed. Though, it's just bad enough to be great riff material.