I will write about Bruce's dream cameo of Flash, so if you haven't seen the movie, don't keep reading, this will have spoilers to both Injustice Gods Among us comic book/game and the Dawn of Justice movies. SPOILERS!!!
We all remember that epic scene with Flash from the movie.
Now what exactly does this cameo mean? While this is only a theory, I am fairly certain what they referenced in this scene and that is the Injustice Gods Among Us game, let's take a closer look.
Flash: "Lois Lane is the key"
Barry is hinting at what happened to Lois Lane in Gods Among Us game where Superman accidentally killed Lois Lane to save Earth from Doomsday.
Flash: "You were right about him, fear him"
Flash here is hinting towards the fact that Bruce was always right about Superman, Bruce as we know hated Superman for destroying Metropolis and wants to destroy him. My theory is that Flash is hinting at Bruce being afraid of Superman as "You were right about him" and tells Bruce it's alright to fear him.
What more we have going for this theory is the suit Barry is using, it looks like some kind of armor suit, the same kind of armor suit he is using in the Injustice Universe.
Injustice will most likely never hit the big screens as a story line. Even if I am wrong about this and this was meant as something else, I am fairly certain Snyder gave a good nod at Injustice with this, it would be too much of a coincidence other wise.
Some people think that they should have some how played this Flash warning into the movie like put Lois Lane in real danger where Batman has to save him or Superman will turn evil. While that would have been great, I don't really care about it, I am just happy I got this cool Flash scene, considering they had a crappy Flash scene later.
Bonus: Jimmy Olsen in Injustice Gods Among us died the same way he did in Dawn of Justice, being shot directly while he was on his knees.