I thought it was pretty good, though it might have been because the reviews were so uniformly terrible. I could see giving it a "C," but not a 30/100.
Some (most) of the dialogue was terrible, but the action improved upon Man of Steel by actually not putting me to sleep. (For that matter, it probably improved on the action in Age of Ultron, and I found that movie generally dull, as well.) The "Martha" plot point was unbelievably awful, though.
I have more thoughts, but not much time right now, so I guess I'll wait till more people have seen it. I will say, though, that for people unfamiliar with the DCU in any medium, I think parts of this movie would be extremely confusing.