DC Extended Universe - Batman v Superman preview comic books introduce us to the characters and offer a little insight on the plot
DC and Warner Bros. have a lot of catch up to do with Marvel regarding the amount of characters in their cinematographic universe, and even though it seems that the Batman v Superman: Dawn of Justice movie will include an excess of characters related to the Justice League that could be lost in this chaos (I hope not and that they turn out with a better way than Marvel Studios to put all these stories together), DC correctly decided to introduce its five leading characters and certain elements of the plot, like the political theme, in individual comics for each character, if you want to read these comics you can do it in this website, I would only summarize what I consider most relevant:
In most of the comic books there is a constant element, Lex Luthor. Although many people, after watching the trailers, consider Lex as the funny character of the film (and this might not be far from true) in this comic books we have to realize that this character will be truly despicable. We see that he has eyes on both heroes, probably more on Superman, and that he introduces himself to the media as a kind of hero to the Metropolis population, but when asked if he is a hero like Superman he says that he's not, he is different. Lex's personality is interesting, we know that he's the bad guy, but he displays himself as someone kind, with concerns for the people, buying companies to open more working opportunities, investing in the city, etc., but it seems that everything he does is actually in his own benefit, because he can later sell such companies or lands to a much higher price than the one he paid, and/or use such lands to experiment with Zod's corpse, in Lex's possession.
In the comic books that focus on Superman and Batman their personality is evident, we confirm what was already known, a long time ago Batman was a nice “vigilante”, capturing criminals and lending them to the police, now, since the Metropolis incident, he’s a vigilante that leaves the criminals ready for months in physical and maybe psychological rehabilitation before even being able to face trial. Superman is the nice guy that helps people wherever he’s needed but only if there are not political issues at stake.
Things get interesting on Senator Finch's and Superman's comic books, that show us the political and social issues that the existence of someone like Superman brings to the table and that I hope it would be more explored in the movie and not just in the comic books, yes, I know most people doesn't want to see politics in a movie about a guy that dresses up as a bat vs an alien who could destroy a city on a whim, most people want to see a fight between the heroes, to see Wonder Woman, the future members of the Justice League, Doomsday, etc., but DC has promised us a better plot and a more “real” world than those of Marvel, and by the way they managed their initial promotion I want to see the sociological, political and moral issues in the movie.
Superman is the object of discussion both in the entertainment media as amongst the military and politics, there are those whom consider that he's doing right and that he should be left alone, to let him act freely because he has done nothing but saving lives, without mingling in political issues as backing up specific countries, because it could lead to war situations; on the other side there are those whom consider that Superman cannot remain external to this situation, what if the best way to save lives is mingling in the political issues, disarming countries, entering in conflict zones and “cutting heads” of the terrorist leaders, wouldn't this be more helpful than stopping a train from derail? And there is also the human side, every person that ask him for help even for silly things as paying the rent up to the ones who ask him to cure them of cancer or the ones who think that there's a conspiracy, being Superman the first of many aliens that will come to form an army to conquer Earth (even though he already saved them from Zod and his followers).
I found very interesting that DC jumps deep into this tangible, elemental, question: what is society's reaction to an alien, a very powerful one. Unlike what Marvel and their MCU have shown, it's unreal that people live peacefully with the idea that someone like Superman exists, there are many conspiracy paranoids, there would be many religions founded in his name, etc. I just hope that this issues are treated in the movie and won't be left aside to a 5-minute mention. I think those issues could be the big difference and what could make DC beat Marvel, we already know they can make a really good action film with Man of Steel, and that the powers of their heroes are those of the gods, that's not what interests me, I want what they promised and that they brag will be their difference with Marvel. At least these comics seem to indicate we are going in the right direction.