It seems unlikely that two such similar films would come out at the same time without Marvel and DC doing it on purpose. Batman v Superman: Dawn of Justice (released March 2016) is about whether or not heroes are given too much power, created by the popular superhero company, DC comics. [Captain America: Civil War](tag:994409) (released May 2016) is about whether or not heroes are given too much power, and is created by the other popular superhero company, Marvel Comics. Despite allegations of these movies being the same, to what extent are these two films offering something different?
1. They have individual tones
Well for one thing, as with past films, we can tell that DC is going much darker with Batman v Superman than Marvel is with Civil War. Just by comparing the lighting in the trailers, and the sorts of things the characters are saying, we can tell that Batman v Superman is going to be darker and grittier than Civil War. Marvel films often look brighter and glossier than DC films, and DC films often have darker themes and even just the lighting in general. They both have very distinctive styles.
2. The number of major characters/superheroes
Other than tone, the biggest difference between the films is perhaps the number of participating heroes. Whilst Civil War will have somewhere around a dozen heroes picking a side and battling it out, Batman Vs. Superman will have the two protagonists and three or four other heroes. This approach will give each character more screen-time, but Marvel's approach will bring in more heroes that fans want to see such as Spider-Man and Black Panther.
3. The character conflict
Another big difference seems to be the cause of the fight itself. Whilst Civil War is about keeping heroes under control and monitored, Batman Vs. Superman is more about the worry that Superman has been given too much power. For this reason, Batman Vs. Superman is going to be a lot more personal, as Batman will feel that Superman is a threat, and Superman will feel insulted/threatened by Batman. Although on some level Civil War will be personal because the two characters have been grinding each other's gears for quite some time, the fight comes down to difference of opinion and belief, which is why each of the other heroes pick a side.
4. Time spent on context and setting
While most of the characters in Civil War are already acquainted and have opinions of each other, Batman and Superman don't know each other, making them perhaps more hostile. For this reason, DC will have to show an introduction and conflict between these two characters, whereas Marvel already has this covered - they can jump straight in with the main events of the movie.
Batman Vs. Superman is likely to be much more impartial than Civil War. Being a Captain America film, Civil War is likely to focus primarily on Captain America, with less focus on Iron Man's argument. Furthermore, the audience is more likely to side with the protagonist, meaning that it's not going to be very even argument. Batman Vs. Superman will be more impartial, with both protagonists getting (near enough) equal attention.
So, the two films might seem incredibly similar on the surface, but when you look a bit deeper there are a lot of differences that define the film's individuality. A lot of these film's differences comes from difference in production company (Marvel or DC) and both will have a look unique from the other when they hit the cinemas. We don't know which will be more successful, but they'll both be good in their own way.