I mean, apart from the fact that Dexter indirectly caused her, in his words in a eulogy(!), "brutal death" at the hands of John Lithgow's Trinity Killer(possibly one of Lithgow's more committed, and definitely most frightening, performances). Rita was annoying, to most fans of Dexter and to myself, though acted quite well. The problem was that she became fairly one-note once her criminal ex-husband was out of the picture. From that point onward she gives the appearance of one-note yammering about whatever self-help book or TV show she saw that day, all focused on becoming the most perfect suburban middle-class family, acting in every way as such people are supposed to do.
But if you shift perspective, there's an aspect to this that Dexter and, I think, even the writers may have missed. They never seemed that interested in Rita's inner life, though they're certainly interested in Deb's, and Rita's kiss with the neighbor was almost the only thing that she was given to do that, at least at that moment, didn't relate directly to Dexter's point of view. And Deb's inner life is, pretty much, her relationships with Dexter and the "wrong men" she keeps sleeping with, either twisted or doomed. Basically, they were given inner lives insofar as sex was related.
But here's what I think is missed about Rita, and that signifies lost opportunities with her. Why is Dexter, initially, with her? Because she's good cover for his activities. Then, slowly, he gets sucked more earnestly into domestic life. But one major theme with Dexter Morgan is his attempt to seem as normal as he can, and so he tries to learn what humans consider normal things to do so that he can act the part as well as he can, believing himself to lack humanity and empathy, and a grounding in thinking of any of this as a given the way "normal" people do. This, however, isn't so much meant toward getting a happier life as it is--at first--to facilitate his hobby of murder. It's only later--as he starts to learn he does have emotions and does feel empathy, and you'll notice fewer murders--that his domestic life becomes part of him.
The reason they connected, though neither ever realized it(she less than he, though) was that Rita was always doing the same thing as he, only for different reasons. For normal reasons: for the sake of her children, and to assure a happy life for herself as well, after a great deal of suffering and obvious shame(even when happy she always looked a second before or after tears) that drove her from being part of normal society, at least, certainly, in her own mind. So she tries to learn what a normal person does. She tries to improve herself, move into the middle class, live in a nice house in a nice place, be married, reset her life. And not completely comfortably for her; imitating something till she becomes it. The self-help, Oprah kinds of things she would say were annoying, but they still did not come from an unreasonable place: the desire to be as good as she could by society's standards. The desire to be accepted after her abusing, junkie husband drove her to rock bottom. The desire to be, at the least, thought a fit mother.
Rita was the version of what Dexter does that normal people pursue. You know, ones that aren't sociopathic killers.
"Eternity in the company of Beelzebub, and all of his hellish instruments of death, will be a picnic compared to five minutes with me & this pencil." --E. Blackadder, 1789 Questionable
words & pictures from John Linton Roberson