To be honest I think it'll be decent, it won't be very good but it won't be bad. I'm still angry at the second trailer, I already feel like I've seen the movie, and at the end of that trailer Batman and Superman are like allies, completely taking away the fact it's supposed to be Batman vs. Superman.
I think the main issue is that this film is too full of characters we haven't seen in their films yet. We've got Batman without his solo film, Wonder Woman and apparently we might get some Flash and Aquaman, if this is true it's going to be a mess. DC had a real opportunity but they decided to cut corners to get to the Justice League as soon as possible. I just don't see it working, but focusing on this film I think it'll only be ok.