I really don't understand why, we already get those light-hearted fun with Marvel. Do we really need DC doing the same? I love the dark approach, it's different and more interesting (to me).
Hmm, we don't "need" any tonal changes, just it's an uphill battle whenever you're trying to change the way people perceive certain heroes or go for a more serious take. If you have a goal like that then you better make sure you can sell it. Hell I just watched the first iron man again and Tony kills like 5 people with a shoulder canon, then blows up a missile that ends up killing all the bad guys (Terrorists in this case) without batting an eye or showing remorse. The reason people accept that is because there is no image of iron man in their head, and the film doesn't reflect on how inherently awful of an act killing someone like that can be. They just roll with it like it's normal.
I'm not implying BvS's reception is only because of it's tone or anything like that of course but I think what Snyder is trying to accomplish with his films is overly ambitious and some people feel he doesn't have the chops for it. He should tone it back down to like Day of the Future Past level of storytelling.
As for BvS's WoM, I think there are some people out there that have an unhealthy obsession with this movie, even before the first trailer dropped, due to Man of Steel. BvS was like the day of reckoning for them and they went with it full throttle. It's easy to tell when the most negative threads are essentially echo chambers of 5-6 people with a few new faces popping in every once in awhile. I've never seen this level of vehemence, it even makes Man of Steel look tame. I don't doubt that it's turned some people off the movie and that can have a damaging impact when WoM is exponential on some level. Throw that in with a confusingly edited, overly ambitious movie that runs a little dry on action, and its hard to spot people that absolutely loved it.
My friends (not necessarily fans of MoS or DC) say the critics were overly harsh (I'm assuming they couldn't distinguish between RT% & Average rating) and said it was either ok or good, but they weren't raving about it on facebook or twitter.