The title really says it all. I've seen some discussion on the movie recently, and the general consensus seems to be that it's like the worst thing ever. When I watched it I can honestly say that I enjoyed it, yet this film received terrible reviews, and I've seen some people say that it should be retconned entirely for the sake of the Justice League movie.
So what makes this movie so terrible? Seemed like a fairly standard superhero movie to me. Met my expectations just fine.