Batman and Superman are arguably two of the most popular superhero icons of all time. They've had many movies about them and both had TV series's so it was no question why WB would make a movie about them going face to face.
WB have done many attempts on doing a Batman vs Superman movie, but never really green lit any of them. There is even a terrible script on one that was almost going to be made in 2003, but as you've guessed already, it sucked.
So if the script and story they have now is any good, why did it take over a decade to get this movie off the ground? Like the new Fantastic Four movie, they've tried many times to get a decent movie made but maybe, just maybe, there is just no good story to get the Fantastic Four together on the big screen like how there is just no good story to get Batman and Superman together on the big screen.
Now look, I very well could be wrong, but why else did WB take over a decade to get it made, plus one more year after the date changes. So, do I want this movie to suck? Heck no! I'm looking forward to this more than my own birthday! It's just I am worried for this film. But if it does bomb, I am sure WB will not go on to making any more DC films. If it ends up to be like a mixed reviewed movie like Man of Steel, then they might continue on.