Again, the Nolan films are pretty darn "dark" and "serious," overall (although not completely humorless), yet all three (yes even TKDR) were critically acclaimed/well-received and also popular with the GA.
Most of the Bryan Singer X-Men films are pretty "dark and serious,"(although again not without humor), yet they've been well-regarded by both critics and GA (although the new one seems to be getting a more mixed reception, but not really because of it's tone).
The last two Captain America films, which as far as Marvel films go take themselves much more seriously than many of the others (and explore more complicated themes/ideas to boot) are two of the most acclaimed ones from critics, and the GA loves them as well. And do son and so forth.
So this idea that the critics, or the GA, don't like Snyder's movies because they're "too dark and gritty" or "not enough like Marvel" just doesn't hold up. Heck even MOS wasn't completely panned, it's just really controversial (which by it's very nature means that there are also people who really like/love it and stick up for it). But BVS, people don't like that because they don't think that it was good or holds together very well.