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.
Fridge Brilliance: In the "Marvel Werewolves" reality that Ash gets sent to at the end of the Army of Darkness crossover, he's dropped into New York right as the werewolves are devouring Galactus. However, in this group, Iron Man has been quietly replaced by Black Widow, presumably because as a werewolf, he couldn't fit into his suit and thus had nothing special going for him.
Fridge Horror: Zombie Morbius impersonates the real Morbius for about two weeks. His disguise? A latex mask and gum to keep it in place. Now, even in the comic, it was kinda obvious that there was a noticible difference between the real Morbius, who looks pretty ugly because he's a Butt Monkey, and zombie Morbius, who looks even worse because he's an zombie and a Butt Monkey. In that two week span, didn't anyone notice that Morbius looked a little different? Or maybe notice the smell a walking corpse must have made? Or that he looked uglier than usual? Or that his body temperature was a little colder than usual? The horror comes in when you realize that for no one to notice, Morbius, even "normal" Morbius, must be really, really ugly and smelly and cold for no one to notice that a freaking zombie replaced him!
After over forty years of angsting over his fate every time he eats somebody, why did Spider-Man never kill himself? He knows that destroying the brain will work. It is possible that the Hunger Gospel simply won't let him.
Hilarious in Hindsight: Marvel has always said that the Ultimate and mainstream universes won't Cross Over, as it would show that they had run out of ideas. The Marvel Zombies were introduced in the Ultimate universe, and then wound up crossing over with the mainstream universe during a Fantastic Four arc (from when Storm and Black Panther were replacing Reed and Sue), and Marvel Zombies 3 was about the Zombies trying to invade the mainstream universe.
Holy Shit Quotient: If overpowering and consuming the freaking Galactus like they did in the first series doesn't constitute as one, we don't know what does.
My Real Daddy: Fred Van Lente redeemed the series after the disappointing Marvel Zombies 2.
Sequelitis: Marvel Zombies 2 is widely seen as a step down from the first book. 3 and 4 are generally seen as pretty good but not as great as the original. 5 is a Base Breaker; some people like it (especially since it resolves the plot points set up in the 3 and 4), others think that the concept has overstayed it's welcome.
Squick: Wasp and Reynolds (not the Sentry, but one of the Acolytes) fall in love. Okay. They eventually share a kiss. Okay. But one little detail: she's a zombie.
In Marvel Zombies Return Spidey, due to some not better-specified "muscle memory", ends up using his veins and arteries as webbing.
The Woobie: Spider-Man is tormented by his status as a zombie, especially since the two people he ate first were Mary Jane and Aunt May, which overwhelms him with guilt. Although his torment annoys his companions, who view it as Wangst, unlike the others it's what makes him the only zombie to really retain at least some semblance of his former humanity besides Doctor Doom, and aids his eventual Heel-Face Turn and redemption.
Though he doesn't seem to mind devouring J. Jonah Jameson: