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.
YMMV: Marvel Universe
Adaptation Displacement: Blade. More people are familiar with the movies then with the comic book character, up to the point where Blade was all but turned into an African-American in the books to better match up with Wesley Snipes portrayal.
...wait, what? He was always an African American, wasn't he?
He is African-English. He was born in London.
Alternate Character Interpretation: The Wasp. It's very easy to read her early stories and interactions with future husband Hank Pym as being that of a manipulative, exploitative bitch who ruined her partners confidence by leading him on then switching her affections to another team mate, taking advantage of a recently widowed man by playing up her resemblance to his deceased wife, and making light of his insecurities.
Continuity Lock-Out: Frequently, and is, along with the DC Universe, one of the biggest poster-franchises for this trope.
Crapsack World: Especially prevalent in the X-titles. Even worse, Bad Futures seem to be the norm among those that have been explored via Time Travel. One thing the Marvel Universe cannot possibly be described as is "optimistic".
Crazy Awesome: Dr. Pym can be an amazing character when written well, unfortunately so few writers know what to do with him.
Crosses the Line Twice: After Frank Castle killed third-string villain Stilt Man (with a bazooka shot to the groin no less) a group of other less notable Spider-Man villains held a memorial for their fallen colleague at a local bar. Frank made sure they were all there, then blew up the bar.
Ending Fatigue: Roderick's story went on for several years with two unmasking teases before picking a character who was already dead to be him (later revealed to be a fake 10 years later).
Foe Yay: Mr. Hyde's obsession with the Cobra, his former partner in crime, verges on this.
Fridge Brilliance: Phil's descent into insanity and his Face-Heel Turn actually make a lot more sense than you'd think when you consider that people who take the Goblin formula often suffer from mental instability. Roderick Kingsley modified the serum he took so it wouldn't drive him crazy... but Phil wasn't so lucky.
Electro's star mask looks goofy to some people, but it's so distinctive and such an iconic part of his character that it's hard to imagine him without it. Even after he loses the mask, he gains scars on his face that have the same pattern. His Ultimate version really loses out for not having the mask.
Suffice it to say that Macendale was a very poor substitute for Kingsley.
Macdonald Gargan. "A loser dressed like Venom is still a freaking loser."
The Scrappy: Anti-Venom has not exactly been well recieved.
Unpopular Popular Character: Although he's come to be seen as something of a loser in the supervillain commmunity, the Shocker nonetheless has a sizable fan following. Ironically enough, it's his lack of a Freudian Excuse or obsessive vendetta with Spider-Man that make him stand out among Spidey's enemies. And as this profile shows, Shocker's actually defeated Spider-Man more times than you might think.
Bob Budiansky wrote 8-Ball as a clever, dangerous criminal with a wicked sense of humor. Later writers made him yet another in an endless line of disposable C-List Fodder. What a fucking waste...
Jason Macendale basically lacked everything that made the Hobgoblin a good and unique villain in the first place. To illustrate how bad a villain he was, he once made a Team Rocket exit after a fight with Spider-Man when the latter was 'drunk!' It got so bad that Roderick had to come out of retirement and kill him to preserve his reputation.
Dr. Pym. First wife, dead. Second wife, dead. His robot son? Genocidal killing machine. The only robot son that wasn't genocidal? Killed by his genocidal brother. Best friend, Bill Foster, murdered. Other best friend, Scott Lang, also murdered. Just about anyone he ever cared about has wound up dead. He's had at least four documented mental break downs and all of his inventions have been turned to criminal use, tarnishing his scientific legacy. It doth suck to be Hank Pym.
The X-Men as a whole are a team of woobies, and the mutant populace by extension. Even the most upbeat and innocent characters like Nightcrawler, Kitty Pryde, and Pixie tend to go through a lot of hardship, while mutants as a whole have faced countless atrocities against them, including legalized enslavement and even state-ordered genocides. Its even worse for civilian mutants as they often don't have powers that are actually useful or even threatening (in some cases, they don't even have 'powers' at all! Just physical mutations), but are stilltargeted for being 'freaks' by thugs and giant killer robots alike. Being a mutant means that you'll forever have a target on your back, but the 'cool powers' aren't a guarantee, and judging by the informed numbers of mutants compared to who we see, its a safe bet to say that most mutants don't have the kind of powers that can protect them from mob violence or giant robots.