First off Jennifer Hudson's character "Louise from St. Louis" was both interesting and problematic -- she fulfilled a much-needed diversity quota on the show, but she definitely came of as flat and underdeveloped as a character. I'm going to outsource my analysis on her character to The Root's piece on the BBF:
In August 2007, Greg Braxton of the Los Angeles Times first coined the term BBF -- black best friend -- in the article "Buddy system; They're wise, loyal and often sassy. Black Best Friends help white heroines, but do they limit black actresses?" One unnamed source joked that celluloid BBFs should form a support group to save "woefully helpless white girls."
Here are the specs on the BBF: "They are gorgeous, independent, loyal and successful. They live or work with their friend but are not really around all that much except for well-timed moments when the heroine needs a dining companion or is in crisis. BBFs basically have very little going on, so they are largely available for such moments. And even though they are single or lack solid consistent relationships, BBFs are experts in the ways of the world, using that knowledge to comfort, warn or scold their BFF."
Of [Jennifer] Hudson's "bossy" Louise, one article said the character had "an uncanny ability to help her boss get her life back in order."
Spoilers ahead: For me another problematic part of the movie (and there are so many) was Carrie's relationship with Mr. Big (full disclosure: I pretty much hate Mr. Big; I find him ugly, boring, and generally crappy as a character). Watching the two characters continually break up and get back together was something akin to watching an emotionally abusive relationship, fundamentally because the way the two characters are written they are emotionally incompatible.
Take the wedding: Carrie begins with a small wedding, but since she's a fashionista, the wedding quickly becomes about designers and it-list guests. Big refuses her, it seems based on the fact that he cannot suffer through an overly expensive party. There's even one point where Carrie blames Miranda for Big's decision to leave Carrie at the alter. As if Miranda had given her 10 years of emotionally distant non-commitment, not Big.
In the end Carrie goes back to him and they end up doing the wedding his way: in a courthouse. In one episode Carrie wonders if she's a masochist because of her emotional back-and-forth with Big. He has all the emotional power, and Carrie can never seem to cut ties altogether. If Carrie were a real person (and I know that this is a stretch) it would be hard to watch her go back to someone who kept her at an emotional distance when that is clearly not what she needs. It's hard to watch a character go through the same problem over and over again, then somehow be expected to be happy they end up together. This is one case where a Hollywood ending really wasn't appropriate.