Its a Zack Snyder film, so no matter how good it is many critics wont risk 'cred' by giving it a good score. So I expect a low 70s RT score mostly thanks to Ben Affleck being in it and a dialogue heavy Chris Terrio script.
We've only really had one such other big movie launch at the same time of year and that was Captain America the Winter Soldier. It hauled in 700 million thanks to being a sequel, having great reviews, and the Avengers bump.
So we have to factor in how Batman v Superman compares to the Winter Solider.
Captain America 2 scored 89% on Rotten Tomatoes. Theres no way Batman v Superman scores that high. Critics dislike Zack Snyder films, he only has 2 movies rated higher then 60% on Rotten Tomatoes.
However I believe the addition of Ben Affleck (star power in a major role) and screenwriter Chris Terrio (who will write a film closer to oscar bait then fanboy bait like David Goyer) will help the film's RT score. So I predict a RT score of 75%.
So because I predict it to score about 15% less then Winter Soldier on Rotten Tomatoes that loses the film some money.
So we go from a 700m worldwide gross to 650 million.
Next is the characters. Superman is more popular then Captain America, so is Batman. Then there is Aquaman who will have a major role. And of course the first apperance of Wonderwoman.
So,
650m current then,
+75m for Superman
+100m for Batman
+40m for Wonder Woman
+20m for Aquaman
= 885 million
Then,
+ 100m for Batman and Superman on the screen together for the first time hype
= 985 million
+15m for Hans Zimmer score
=1 Billion
So there it is, I think the film will settle down around the 1 billion mark world wide.