Okay for me, the flaws are technical ones that Snyder has always had an issue with: the movie length, the editing, the pacing, and some narrative issues that he tries to smooth out to varying degrees of success and that has a lot to do with the editing and pace. The good is that it is a logical extension of what happened in man of steel rather than trying to act like that didn't happen, and superman is dealing with his own issues because of that. He's trying to figure out how to be a hero and what is the true meaning of what he does if there will always be people who kill him in the press for it. Unchecked power, godlike ability, etc. Batman is good, Wonder Woman is good, Lex has moments of good but then moments of meh or straight up
so he's a mixed bag for the most part. And the action is of course on point as you'd expect a Snyder movie to be and it does set up some very interesting things for the next round of movies, specifically justice league. It might be the closest to comic book batman on screen but yeah it is a dark movie. There are brief moments of levity but it's not concerned with that and that clearly is an subjective thing