I generally don't discuss Marvel films just as a way of budgeting my time, but I found this interview fascinating:
"
How Age of Ultron Nearly Broke Joss Whedon" via Vulture, some quotes:
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[Avengers 2] is an odd film in some ways, Whedon said. We went to some strange places in this one, and making that work and making it flow and making it all feel like it's part of the same movie was difficult.
With so much at stake, there's gonna be friction, Whedon acknowledged. It's the Marvel way to sort of question everything. Sometimes, that's amazing. And sometimes and here Whedon growled his compliment through gritted teeth, the meaning clear thats amazing.
There's one or two things that I'm unhappy about not having in [Avengers 2], but they're small, said Whedon.
When I watch [Avengers 1], I just see 'flaw, flaw, flaw, compromise, laziness, mistake, said Whedon. "The reason I set out to make another film is because I wanted to make one that was better...."
Though he gave his all to Age of Ultron, Whedon hasnt been able to watch the final cut all the way through yet I tried, said the typically hard-on-himself filmmaker, and I had a terrible time but hes heartened by the glowing reaction online from early press screenings. Is it perfect? It is not, said Whedon.
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In context, Snyder isn't as transparent about the flaws he sees in his own films, but he does express frustration with his
own inability to convey his intentions based on viewer response (particularly with
Sucker Punch)... MoS was, in part, an answer to critics who viewed him as only being able to do stylized films filled with speed ramping and slow motion... however, BvS will be his first opportunity to go back and directly address criticisms within the same continuity... and that's without the loving reception
The Avengers received.
A couple of points of distinction between Snyder and Whedon in terms of exhaustion and endurance. Whedon is more of a creator, having cult success with many original properties... Snyder has dabbled, but likely does not have the same ache to create original property, likely finding the canvas of the DCCU enough for now. For Whedon, it's more about paring down all the ideas in his head to do one, while for Snyder, it's about getting to work as much as possible. In terms of relative power, Whedon was able to work under Feige's heel but Snyder is practically in Feige's position at the WB with autonomy to exercise. Whedon gets separated from his family during filming and his family is relatively young. Snyder's family is older, his wife is by his side the entire time, and he incorporates his children into working on the film often. Whedon is only a year older and not unhealthy, but clearly Snyder puts a higher priority on keeping fit than Whedon. Both build lasting relationships with their actors who act as extended family on and off set.
Hopefully, these differences mean that Snyder is pouring / has poured his all into BvS and will have the passion to go the distance with Justice League.