I wonder if most of the negative reviews come from MEN who hate movies where most of the characters are WOMEN. This movie is not just about the Black Widow (#1). It's also about her sister (Black Widow #2), her mom (Black Widow #3) and all the other Black Widows - like hundreds of Black Widow killer babes.
I think a lot of people also hated "Dark Phoenix" and "Captain Marvel". But I love both of them. I consider "Dark Phoenix" my favorite X-Men movie. I must love chick-flicks, especially the ones with hot babes.
Like
@Cos says, "Black Widow" is more character driven and likes to emphasize "family bonding" - touchy-feely.
So "Black Widow" might be a little too much ESTROGEN for most men.