It really is, in my opinion, a simple thing. It all starts and ends with the word 'Batman'. Because he's Batman. I'm not writing this as someone who hates the Dark Knight, or someone who's a fanatic Superman groupie. I love Superman but I admit that his stories are lackluster, to say the least, except when he's in the Justice League or has a crossover even't like H'el on Earth. No, my favorite DC character is Black Adam. So what I'm trying to say is that I will try my best to be unbiased about all this.
And herein lies the problem. People are not and will probably never be unbiased about this series. There will always be who say that DC is going to be a failure because they are just copying Marvel. Or that there should be this Green Lantern, not that Green Lantern, now I don't like it. Or why is Barry Allen the Flash, I want Wally West. We can never be truly unbiased. Personally, I would love to see Kyle Rayner, my favorite Lantern or Wally West as the Flash because in The Flash show running now (no pun intended) gives us a really good Barry Allen already.
It has been, to my knowledge, confirmed that Batman will be the central character of the DC cinematic universe, except of course solo movies. He will be the one who'll get the Justice League together when the world needs it, he will be the one who'll gather them all. Which isn't really a good thing. In my opinion, the JL was great as it was in the New52 reboot. A world was in crisis and these heroes, who knew about each other but didn't really care, were thrown together. This was good. But now, it seems like they were following the Marvel 'Avengers Initiative' thing where there is one person who plans to bring together heroes. This was a chance for DC to stand out but since I don't see the future, this might be just speculating and planning from WarnerBros' part.
As for Batman, well I don't think the character itself is powerful enough (and not in the physical way) to hold together movies like that. He is great in his own movie, but others don't share his grief and darkness, so seeing interaction with others from his perspective could be awkward. That of course is yet to be seen, how Ben Affleck will portray him.
Forcing Batman against Superman (again...) is just boring to me now. I've read many stories when they do fight and then the Dark Knight Returns animated movie came out which was just bullshit (pardon my french) aaaand then Injustice: Gods Amongst Us portrayed Superman as the asshole... AGAIN. Superman is NOT an asshole and he is an even more boring character if he becomes an asshole. Seriously, let's just try to evolve his character instead of doing the old and boring 'But what if he turns on us? Who will be able to stop him?' cliche. It ran it's course. Just let it die. I think Superman deserves better, even though foaming-at-the-mouth rabid Batman fans say otherwise. Henry Cavill played a great Kal-El and I loved Man of Steel even though it had it's flaws.
But how and why will it make a lot of money? Batman of course! Christopher Nolan's brilliant Dark Knight series has made this character even more famous than he was before. Combine it with the Batman Animated Series, which was yet again, great, or the Justice League series where Batman was not only a prominent but we could say, was a lead character and was almost always portrayed as infallible and cool. Combine that with the also brilliant Arkham series in gaming and Batman has won all types of media you can have. And we haven't talked about his well-written comics yet.
Batman is a great character and I love his stories but I slowly but surely have enough of him. I'm getting bored of him and his perfection. Other great characters like Aquaman, Flash and even Superman are thrown into the back because of this. I'm really glad that Shazam is growing in popularity, even replacing Aquaman in the most recent Justice League animated movie War. But to be honest I really hope that DC has a bit more to give us than Batman, Batman and Batman.