What it is it that DC gets so wrong and Marvel gets so right making films?
They do a lot of things better. Marvel has patience. Look at the arc of the three Iron Man movies, the three Captain America Movies, the three Thor movies. Since the first Iron Man movie, we've been watching these movies for eight years now.
Marvel movies also tend to be very character focused. The Iron Man movies is not about Iron Man, they are about Tony Stark. The Thor movies are about Thor the person not Thor the thunder god. The Captain America movies are really about Steve Rogers.
The Avengers movie profited from both good things. Patience let Marvel develop the characters in stand alone features that focused on the specific characters so we would know and care about them. So when the Avengers movie comes out we don't have to develop these characters from scratch: we already know them. We already know the prime antagonist Loki. We already know the core heroes and Nick Fury. We can just let the story flow organically.
But I think maybe the least appreciated thing Marvel does well is something it does because it was forced to. Marvel couldn't make movies about its most popular characters and strongest properties. It couldn't make Spiderman movies or X-Men movies or even Fantastic Four or Hulk movies because of licensing issues. It couldn't make movies about the characters people knew the best. So it had to go to the well and pull up less well-known characters. Which is not to say that Captain America or Iron Man are unknowns, but compared to Spiderman their backstories are less familiar. So Marvel couldn't rely on people just knowing who these characters were, and had to
invent them for the movies. Captain America and Iron Man have decades of twisted conflicting backstory. Marvel had to reduce that down to something simple they could convey on-screen. Marvel seems to be extremely good at taking a character like Captain America and distilling it down to something simple that movie goers can understand. He's a naive eager boy-scout that just wants to fight for his country, and is gifted with the ability to do so but finds the politics of it to be something he didn't expect. He's a straight arrow in a crooked world. Tony Stark is a rich genius with engineer's syndrome: he thinks he can fix anything with technology. But he also has PTSD (from multiple trauma) and guilt (also from multiple instances). Tony Stark is easy to understand: he's tech-smart, but emotionally stunted. His heart is in the right place but he doesn't have the morals or the boundaries that would prevent him from throwing gasoline on a fire to try to put it out. Even Thor is someone audiences can relate to. He's kind of a spoiled child trying to live up to his strict uncompromising father.
Marvel takes comic book characters with fifty years of history, waves a magic wand, and turns them into blank slates. Then they try to extract a core nucleus of character and backstory that neophyte audiences will be able to appreciate and relate to, and then rebuilds their world around that core. Asgard is what it is specifically because it serves to understand Thor. SHIELD and HYDRA exist specifically in the forms they do because it is the world that creates the best opportunity to tell interesting stories about Steve Rogers, super-boy scout. And in a synergy that feeds itself Marvel builds worlds to suit its characters, then adapts its characters to fit that world. Ant-Man is the version he is because that fits into the MCU. Spiderman very obviously is going to be an iteration of Spiderman that fits into the MCU with specific ties to the MCU version of Tony Stark. I have faith that magic in the MCU will be explicitly a version of magic that fits the MCU and provides the best opportunity to tell an interesting Doctor Strange story, and the version of Doctor Strange we get will explicitly be the one that they can tell the best story about within the current MCU.
I guess if I had to summarize all of that, I'd say what Marvel does well that DC hasn't done well or even at all is they are really good world-builders. The characters fit the environment and the story, the environment shapes the story and the characters, and the story serves the characters and the environment. They set reasonable goals for the next step in world building, then execute that goal very well. They do not try to do more than what their world can contain, but they always try to push the envelope of their world outward for the next set of movies to inhabit.
Notably, people complain that the Batman we see in BvS or the Superman we see in Man of Steel aren't the characters we know. But actually, the Tony Stark in the MCU isn't really the Tony Stark we knew either, neither is the Thor or the Cap, taken literally. But you know what? We *like* the MCU Stark and Rogers and Thor. And because of that, we see those characters through a prism where we can see how they touch the comic book material in certain places, and we forgive the fact that they aren't exact replicas because we think that the limited parts they did borrow connect the MCU versions of the characters sufficiently well. We allow that the MCU Thor was "inspired by" the comic book Thor. But that only works if you start with a character worth liking in the first place. I think that's why many fans seem to simultaneously hate all the killing that Batman does in BvS and yet praise Ben Affleck for portraying the character. We like Affleck's portrayal of Batman so we can forgive *him* the fact his Batman does things we think are out of character. We aren't as crazy about Superman's characterization, so we are much harsher about the "fidelity" of that portrayal.