Quite a lot, and it's not really fair. Plenty of people are actually to blame. The camerawork was pretty bad that can be blamed on the cinematographer, the editing was pretty bad (not MoS bad, but pretty bad) and technical supervisors can bear some of that blame, the arrangement was bad (Zimmer's score was great, but someone obviously had no idea what to do with it,) and there were many... many other faults. But directors... well the buck stops there. At some point Zach Snyder gave the OK to what was very sub-par work.
And it's not like he has a storied history. Lots of people liked it, but 300 wasn't very good (it was just gore-candy barbarian war-porn, it didn't have to be good to avoid underachieving.) Watchmen was ok, really well storyboarded actually (I think that's a strength of Snyder's directing.) And Sucker Punch could have been worse...
But the direction the DC verse has taken (and remember, to this point Snyder's the only director involved) is... well at the very least underwhelming. And right now he's really the most to blame for that. Sure, someone at WB keeps not firing him. But they don't care about the quality of the work. They care about money, and they don't get that the strength of the brand ensures monetary success. And don't realize how much money they could be making if the product didn't stink.