The biggest criticism I have of Blue overall is the way the women were written. Many of them had some really solid moments, but for the most part, these characters were simply vehicles for the deeper characterization of the men rather than being whole people on their own.
The women of Blue generally fell into two categories: They were either there for the sex or there to be saved. Many of them fell into both categories, and the characters were at their worst when they inconsistently slid back and forth between the two.
Diane, for example. Connie for another. And Jill for a third. Diane's beginning was all about getting her in the sack with Simone and keeping her there. At the same time, she was a damaged soul--alcoholic, sex abuse victim--who needed Bobby to save her. This served two purposes: it got a hot chick naked on TV with a sexy man and it added a great deal of depth to the character of Bobby who was able to make her world OK. As enjoyable as all of that was (see best romantic pairings), Diane's best moments as a character came after Bobby died and before she got written into the sack with Danny (see worst romantic pairings). She was standing on her own two feet, facing her demons alone, taking the lessons she'd learned from Bobby's love and living her difficult, but interesting, life. Then what happened? Someone decided that wasn't good enough, or we gotta see her ass again, and she got hooked into the single worst relationship in the history of the show. Having Diane sleep with Danny was so out of character for her that it ruined everything interesting she'd become.
Connie, too, was ruined by love. She was the best-written female character ever on Blue when she started out, and for the time before she was written into love with Andy, she was probably the best written female character on any show. She had a very real mix of strength and femininity. She was the female version of Andy, who was the perfect mix of softness and masculinity. Their chemistry as partners was explosive, dynamic, exciting to watch. But it didn't last. Soon enough, Connie began her descent into the "save me" category and got very needy with Theo. She married Andy and her days as an independent, think-for-herself cop were over. Major tragedy, that. Almost on par with Jill Kirkendall, who started out fairly strong, was given the side story of being a single Mom and a dedicated detective, and then inexplicably threw it all away to return to a drug-dealing, abusive husband. Talk about inconsistent.
Other strong women ruined by love: Licalsi and Lesniak (who disappeared after a disasterous storyline) and, to some extent, Mary (Danny's upstairs squeeze).
Donna is almost an exception. Her relationship with Greg provided shock value, afforded wheezing, shy, nerdy guys everywhere some hope and once in a while, she got to be a little more than Greg's dream/wet dream. She got to have props and wear clothes and hairstyle that added a lot to how she told us who she was. It's not much, but it's more than most of the other women got.
Sylvia may have been the only female character on the show who wasn't explored much beyond her relationship with good reason. First, she wasn't one of the cops, so her workaday world was meaningless to the overall story. We weren't tuned in to see how a DA deals with life. We were tuned in to see how cops deal with life, and Sylvia was a part of Andy's life outside the job. For that reason, Sylvia's character was perfect. She was meant to be a torch in the dark depths of Andy's soul and nothing more. Ditto the character of Kelly's ex-wife played by Sherry Stringfield in the first season, and the same can be said of ADA Valerie Heywood, though she didn't have much to light since her man Baldwin Jones wasn't a particularly deep character.
At the end, the writers probably just had to give up on the women. But what was left was sort of interesting. Rita, who began as yet another damsel in distress, did her time in the sack with a coworker, and was a shrew for a spell, ends up being the only female character who survives a relationship in the squad and goes on to be a normal detective. And Laura Murphy ends up being the only female cop who doesn't sleep with a coworker. (She is, in fact, the only regular detective--male or female--who didn't sleep with a coworker, ADAs included.) Sadly, there wasn't much to either of these characters.
The male characters were illuminated not only by the women in their lives but by their family relationships, their friendships, the work they did and, most importantly, their working relationships with each other. The same cannot be said of the women. I consider it a missed opportunity and (in spite of Cagney & Lacy) still unbroken ground in television to explore the unique working relationships women develop in highly stressful, public jobs such as policework, and how a job like that can affect a woman whose nurturing -- and perhaps nature--is in direct opposition to it. It requires a delicate balance, there is constant conflict and yet no one has yet been able to write it well for TV without having the character fall to pieces. (One of the best female cops ever written: Marge in the film Fargo. Pregnant--the ultimate combination of strength and femininity--and using her noggin to catch vicious bad guys. Yup, she barfed, but she didn't need anyone to win a boxing match for her.)