It's been an awesome couple of years. On Marvel's side, we had Iron Man 1-3, Thor 1-2, Captain America 1-2, and the mighty Avengers; and on the DC side, we had Man of Steel, Green Lantern, Batman 1-3, among others.
Marvel made a gamble and boy it paid off handsomely. It started out with Iron Man back in 2008. The new Marvel studio made plans to create their own cinematic universe. It was no easy task. Back then no one would ever believe that a movie about a man in an iron suit can be so successful.
So what made Marvel movies successful? Let's analyze:
Marvel plan ahead
Marvel was not making just 1 movie; they are making an entire universe based on their comic book characters. They felt they should be creating their own movies and not let other studios make them.
Even when their most successful (and iconic) characters were no longer available, they still have plenty of characters. It's a good thing too, since studios and their backers typically tend to go with safer investments. Imagine if Spiderman or X-Men were still owned by Marvel... Perhaps Iron Man, Captain America and their fellow heroes would never see the light of day.
Characters are important
Because Marvel owns the studio, they have complete control over the characters. Character backstories are carefully threaded and they follow their continuity as much as they can. Marvel villains (mostly) are being kept alive, or their fate unknown, to be used in future installments. This is different than the approach DC (or, rather, the studios controlling DC characters) makes. Villains in DC Cinematic Universe tend to last only within the boundary of 1 movie. Man of Steel's Zod, for example, or Dark Knight's Two-Face.
Let's face it, Marvel movies are made for fun. There are a lot of humour and heart with their films. Actors portraying the heroes and villains are carefully chosen to make sure this happens. Paul Rudd's Ant Man or Chris Pratt's Guardian of the Galaxy are prime examples of this.
DC movies are "gritty" and "realistic" (although a man who can fly or shoot lasers from his eyes are barely realistic); thanks in part to the success of Christopher Nolan's Batman Trilogy. They are not fun - they are depressing at some point. Superman kills; Batman lies.
The right casts
Marvel made the first right decision with Downey, Jr. because they realized actors who embody their heroes are important. They must have heart and humour, will need to commit for several movies and have to work together when the time comes. Marvel also made sure that the supporting casts are believable as well. Actors like Sir Anthony Hopkins, Gwinneth Paltrow, Rene Russo, etc. added gravitas and weights to their corresponding Marvel movies.
Marvel Cinematic Universe extends to their silver screen universe. This was unheard of. To have TV shows follow the cinematic universe is not an easy task. Marvel's Agents of Shield is a prime example of this. With the (SPOILER!!) destruction of SHIELD in Captain America 2: The Winter Soldier, it changes the story completely for the TV Show. Imagine a show about SHIELD when there is no longer SHIELD.
DC Cinematic Universe didn't do this in the past, but I suspect it will. With the release of Superman vs Batman (that will be followed up by a Justice League movie), DC has (finally) follow in the steps of Marvel.
The question is, are they too late?