So I did get to see this.
It's not terrible, but it's not really good either.
The opening third is by far the worst. The baby-saving sequence is terrible, the lasso of truth joke is lame and straight out of Whedon's bag of tricks (and to be fair, it was better in Whedon's JL), Affleck was unimpressive as Batman and the suit is horrendous... the new Flash suit also looks terrible. Thank god they didn't change Wonder Woman's. And she just oozes charisma.
The character bits, on the other hand, were pretty good. Affleck and Miller are great as Bruce and Barry, and Barry's interactions with his dad and Iris are also very good. I also liked Keaton, I think they wrote a very believable and relatable older Bruce/Batman, and he delivers. It was a bit funny how they ripped off the Vader-Luke finale of ROTJ, but it works.
Sasha Calle was great as Supergirl, I really liked her character. There was a great story there somewhere, about her imprisonment, her mission, her allegiances... too bad there wasn't time in the movie to explore it all.
The battle against Zod and the sequence with the inverse Flash were kinda meh. Too much bad CGI and a very pedestrian cinematography/photography didn't help those sequences. If they knew they wouldn't get great photorealistic CGI anyway, they should've gone with some sort of ghost-zone effect, just some sort of distortion to mask the short-comings.
There's a lot of very interesting ideas, and a lot of human drama, but I don't think it really connects in the end.