Here are five reasons watching a superhero movie will never be the same as reading the comics. So the list doesn’t go further than five, we will ignore the colorful Joel Schumacher movies and the tragic unreleased Fantastic Four.
1. From Panel to Film
Rarely do we as moviegoers and comic book readers get to see the two mediums come 
together in perfection. Many times, a character isn’t cast precisely or has a different story than the comics. We get a special joy when we see a movie matching the original comic, panel by panel, in each frame, as The Watchmen displays. An even more special occurrence is when we get to see how the movies give a nod to the original comic. In the comic miniseries Secret Service, created by Dave Gibbons and Mark Millar, we see that a villain has begun to abduct all the movie stars, starting with famed Star Wars actor Mark Hamill. In Kingsman: The Secret Service, the movie opens with a renowned professor, who has been abducted and taken to the same cabin in the snowy mountains of Switzerland; the professor is played by the actor Mark Hamill.
Many times, a movie is cast and some of the characters are not exactly like their comic book references, such as Silver Samurai in The Wolverine. Instead of being exactly similar, the movie takes the Silver Samurai’s character and shows him as two entities. One being the emotional counterpart for Logan in Kenuichio Harada (Silver Samurai 1), while Ichirō Yashida is the healing-factor seeking, honor-less robotic-suit-wearing Yashida clan leader. But still, most of the time, we as moviegoers can accept a change or two in a character for it to fit into the universe they are building. For example, Starlord’s father in The Guardians of the Galaxy 2 movie
will not be Emperor J’son of Spartax, as he is in the comic book universe. (We won’t even mention Deadpool from Wolverine Origins. Though, I just did . . .)
2. Costuming
The gear and uniforms of the heroes and villains as they appear in the comics make sense to the readers because they are meant to be colorful, and we have accepted that in the comic book universe. Heroes and villains are identified by their uniforms after all, right? But with the movies, we want them to be realistic, and realistically, Wolverine’s bright yellow-and-blue spandex in any of the X-titles just would look silly on screen. In the X-Men saga, the X-Men have forgone their colorful uniforms and instead went with leather-accented ones with colored trim as a nod to the comics. The distancing from the comic book source for uniforms isn’t always true, and in some cases, it is just a different continuity that was being pulled for sources. Another example is that Spider-Man’s classic red-and-blue suit makes the transition in Amazing Spider-Man as well as Spider-Man. (However, Spider-Man isn’t a perfect example as we see the on-again, off-again use of Peter’s web-shooters device that he invented and his radioactive side-effect wrist web spinners, which are just pulled from different continuities and universes.)
But sometimes, we get the best of both worlds. A suit that is both realistic to the real world and looks like something the comic book character would also wear. In the Nolanverse Batman movies, Bruce’s R&D division develops various suits of armor that are good for fighting the average criminal or spelunking (Batman Begins), which evolve to be more flexible with segmented armor (Dark Knight). Even the tech and vehicles like the Bat in Dark Knight Rises look like it would fit right in the comic book’s Batcave.
3. Mining the Source Material
The beautiful but anxiety-inducing part about being a comic book reader is that some of the best arcs take months and even a full year to complete. With more and more comics coming out on a weekly and biweekly schedule, we get to see story arcs unravel faster than they used to. The comic Civil War took half a year for one of the greatest stories from Marvel to climax (from July 2006 to January 2007). But this was a half-year-long journey that tied in every comic title in the stables from Marvel. This gave us nearly twenty-seven weeks of stories that further detailed the comic’s arc. From the minutest heroes like Cloak and Dagger 
being thrust into pivotal roles, to the epic clash between Stark and Rogers, there was plenty of story to be told. With the movie Civil War coming out soon, we will not get a story that is nearly as in-depth as the comic book original arc (screw Marvel’s Secret Wars redux of this arc). The hours spent reading through every tie-in and every obscure comic I would have otherwise never read (She-Hulk #8 and #9) are going to be summed up in a two-and-a-half-hour movie with nowhere near the epic roster the comic has. We had a half-year to read through ninety-eight comics (tie-ins, epilogues, and Fallen Son included). That’s over 2,100 pages (assuming each book has twenty pages), and even if you read through a book (I mean fully read it, enjoy the panels, take a full look at the art, and understand the dialogue), you are reading a book in about fifteen minutes, that’s just under twenty-four hours of reading, nonstop!
But sure, a 2.5 hour movie will be able to fully detail the beginning of one of Marvel’s greatest hero-on-hero wars. This isn’t the only movie to sum up an arc in just a short (comparatively) showing. The Dark Knight Rises took the Knightfall arc and No Man’s Land run, performed some gruesome surgery and took out the parts it liked, and Frankensteined it together to create the tale. Turning two source books into one movie worked on screen, but the hacking apart and leaving out some important characters and moments from the inspiring comics were a shame. Hopefully, we can see both those stories in their own movie in the future (regardless of length).
4. Casting the Perfect Superhero or Villain
Generally, the personality or tone of a hero is the main story that we follow in both the movies and in the comics. So far, we have seen that in the upcoming Deadpool movie, the title character is breaking the fourth wall and keeping with his fractured-minded humor. Even if you have read only one Deadpool comic book, you can clearly see that the Merc With a Mouth appears to be an exact replica of the comic book version. (More to come after seeing it.) Another perfect example of this would be Robert Downey Jr.’s nearly perfect portrayal of Tony Stark in Iron Man. There are plenty of examples of times the movie’s casting is perfect and the
actor turns in more than just an inspiring rendition but a duplicate of the comic books. (Side note: A perfect example of the comics coming to life is Vin Diesel’s voice acting for Groot. Man, he really nails that one.) There are times when the movies totally fail to take the mindset of the characters from the comics and move them to the Hollywood versions. Eddie Brock in Spider-Man 3 (they never had real titles for those movies?), was played by Eric Forema . . . I mean Topher Grace. In the Marvel Comics, Brock is the opposite of Puny Parker. He is a tall, well-built, and muscled journalist who looks like he could kick some butt without a symbiote suit. Topher Grace acting as Eddie Brock just made him 
look like a second-place loser who was just as scrawny as Peter was.
To take the 2007 movie even further as an example, Venom himself is a ruthless and violent version of Spider-Man that is super powerful and nearly unstoppable (minus the whole weakness to sonics). He is terrifying in the comics, and when he graces the covers of issues (Amazing Spider-Man #346 and #316), you believe he is going to kill Spidey. In the movie, he just seemed to have a mean streak to him, but wouldn’t actually kill someone. He lost his edge and lost the fans. At least Eddie Brock had the same name; Catwoman didn’t even try with Patience Phillips.
5. No One Is Safe From Change
It isn’t just the Big Two comic universes that make us sigh. We see smaller comics come to life on the big screen, and they don’t get nearly as much grief for their wrongdoings as DC or Marvel do with their film franchises. A comic book from a 
minor publisher is more than just a title. Sadly, we see the general concept of a comic book and the title as the only references to the original book when it makes it to the films. Kick-Ass is a good example of turning a lesser-known comic book into a major motion picture. Sadly the end of this movie got out of control; events and characters don’t mimic what occurs at the end of Mark Millar and John Romita Jr.’s series. When Kick-Ass 2 came out in 2013, the names and premise were the same, and a handful of scenes made it to the movie, but the comics’ general overall tone of blood and violence was tuned down, even though it was still rated R.
Hit-Girl still slices and dices, but there is a sense that the movie just used the base ideas of the comic, and instead decided to go the way of Game of Thrones (having characters act differently just for audience appeal). One of the newer Disney flicks Big Hero 6 sees Baymax, one of the main characters, Baymax, go through an entire rehash of the original superhero. In the comic series Sunfire & Big Hero 6 #1, Baymax is a science project (still the same) that is a robotic sythformer (can change his appearance into any form, mostly as a powerful fight-ready green battle dragon).
The movie that Disney pushed out was a fun Disney version of a superhero movie with Baymax being a lovable form-changing pacifist guardian balloon. Only through changing computer chips does Baymax show any battle-hardened experience and willingness to fight. Disney’s Big Hero 6 took the concept and names and made it into a family animated movie (I’m not upset about this, but it’s important to note the changes from the original).
In the end, if you want to watch a comic book movie adaptation (key word), you need to steer clear of the Big Two (DC and Marvel). With a miniseries or small arcs, some of the older lesser-known comic book movies provide the same experience in theaters as with the comics, such as League of Extraordinary Gentlemen, The Crow, Sin City, and 300. Without having to worry about spin-offs (though some did have them), smaller-run comics don’t have to consider the long history and stubborn mindset of comic fans. Frankly, we are just happy to see these great minor comics come to life.