The release date of 'Batman vs. Superman' is still a long ways away, so it's understandable that there hasn't been too much concrete information released about the highly-anticipated film. Still, there are a few bits and pieces of information from various sources, but it's important to note that many of these are only rumors at this point.
One of the reasons why there's so much speculation is the huge amount of characters involved in the film. Despite being billed as a Batman versus Superman showdown, 'Dawn of Justice' is expected to lead in to the eventual 'Justice League' movie, and as such will include or build up characters that will appear in that film.
Aside from Batman and Superman, characters such as Wonder Woman, Aquaman, and Lex Luthor have been confirmed, though how large their roles remain uncertain at this point. Also rumored to be in the movie are The Flash, Cyborg, and more recently, Doomsday and The Joker.
The Joker rumors are no doubt influenced by the announcement of the 'Suicide Squad' movie where Lex Luthor and The Joker will reportedly figure in major roles. It's highly unlikely that The Joker will appear in BvS as he is more of a Batman villain, but the same cannot be said for Doomsday. Doomsday is, of course, a villain that killed Superman in the comics. Still, it's all still conjecture at this point so take those rumors with a grain of salt.
In more official news, Aquaman's look in the film was revealed by Zack Snyder, and it scored major points in establishing a more "bad-ass" version of the character. Aquaman's movie look eschews the comic book's green and orange color scheme and opts for a more stylized effect. It's a different look for the character, but it fits right in with the aesthetic developed in 'Man of Steel'.
Another look that has stirred plenty of debate is that of Gal Gadot, who will play Wonder Woman in the film. The most common criticism has been of her slim figure which some view as ill-fitting for an Amazon warrior. Still, Gadot has been hard at work in addressing these issues and has been working out with her trainers to gain the physicality expected from the role. A few photos of Gadot whilst working out can be seen in this article at Screen Rant.
'Batman vs Superman: Dawn of Justice' is scheduled for release sometime next year.