Personally, I think that the studio should take more blame than Snyder... though there seems to be plenty of responsibility to go around. I see the broad strokes of this movie to be a big mistake, and I imagine most of those things were out of Zach's directorial control.
The whole "Batman v Superman" thing is, in itself, a seeming attempt by WB to bring in a character more palatable to the GA. Adding Doomsday also seems like a studio decision, as he is part of the (if not the) most popular Superman arch in the past 20 years. Ben Affleck's casting (which turned out well luckily). [BLACKOUT]The forced set up of JL.[/BLACKOUT] Maybe those were Snyder's decisions, but I just suspect not. If they had told Zach, "sweet, well where do you want to take Superman next? Let's not rock the boat and just make a solid sequel," then I suspect things would have been different.
The frustrating thing, of course, is that they had wayyyy toooo much time to right the boat on this one. The film has been largely finished for a year. They could have easily done reshoots and retouches after seeing the final product. That's where I think Zach's real failing is. Nolan seemed to have the ability to control the story how he wanted... he was involved from the start with the screenplay all the way to the end, and you felt like it was his steady hand that was guiding the whole operation. With Snyder, I don't get that feeling. I get a sense of him giving up, like saying, "this is what I've been asked to do, so I'm gonna make it look as cool as I can, and follow the script to the letter." Where's the insistence on quality story telling? Where's the push back? Who was there to say, "stop, this needs to be changed." I suspect no one. They got on a track, and they followed that track right into this. Someone needs to take this thing by the horns and focus on making a compelling story, not a plot by the numbers / follow the formula sort of approach. It really seems like WB doesn't understand their property like Marvel does theres.