Probably best known for starring in Eve's Bayou and the Netflix show Greenleaf, Whitfield is one of those actresses whose talent is greater than her number of credits.
In the lead role, Lawrence is no Eddie Murphy. As written and performed, Darnell comes off as an insecure misogynist who sees any woman as fair game, and refuses to have his advances denied. The opening sequences show him breezing though various women with no care. This montage is intended to set Darnell up for a fall, but for us to root for him there needs to be something redeemable about him - and there really isn't.
The big saving grace of this movie is Lynn Whitfield. Sometimes you watch a film where there is one performance that is not only good, but manages to elevate the whole enterprise beyond what it is. Whitfield's performance is so good because it gives the movie a real dramatic spine - unlike Darnell, Brandy has a genuine reason for acting the way she does, and Darnell is such a self-absorbed asshole that - for most of the second act - it is easy to see Brandy as the story's real protagonist. Whitfield's performance provides the movie with its only sense of dramatic escalation, while Lawrence never manages to flesh Darnell out.
By the end of the film, it becomes pretty clear that Whitfield is so much better than it deserves. But because she is so good, she makes the movie far better than it has to be. It is also worth watching just for the spectacle of comparing Whitfield's nuanced, wounded portrayal of a woman scorned against Lawrence's cartoonish buffoon. It is as if Sigourney Weaver starred in an Adam Sandler movie - the disconnect between the leads is that stark.
Maybe if Lawrence was not the auteur of this movie, it might have been more fully-realised. There is a good movie here, but it needed a different director, someone who could have figured out the tone and given Lawrence the space to build Darnell into a fully-realised character.
My favourite scene in the movie is when Darnell confronts Brandy in hospital after she has made him out to be a woman-beater. Whitfield begins the scene indignant at her former paramour's disregard for her. Once the police arrive to take him away, on a dime she turns into a traumatised victim unable to let go of her abusive lover. As soon as he is out the door, she snuggles back in bed. It's brilliant, and the one time that the movie hits the darkly comedic tone that Lawrence was aiming for.
Regina King is another actor who is better than this movie - she plays Darnell's one female friend, Mia. As with Whitfeld, she grounds her subplot and gives the movie some credibility. She's so good I actually bought her chemistry with Lawrence.
Because both female leads are so good, I just started reading the movie as a meta-textual hostage situation in which Whitfield and Regina King worked together to steal the movie out from under its star.
The rest of the cast are a mixed bag. The recently departed Della Reese plays Darnell's mother. Apart from Brandy she is the one character to call Darnell on his crap, but she does not get much to do. RnB singer Bobby Brown plays Darnell's best friend, and somehow manages to be even more odious in his relations with women than his friend.
Overall, I cannot really call A Thin Line Between Love and Hate a good movie. But it is interesting to watch, particularly in light of the ways that rape culture has finally breached the cultural zeitgeist. The filmmakers intended the film as a response to Waiting to Exhale, but in the end A Thin Line Between Love and Hate feels just as self-righteous and ridiculous as a troll's response to a Roxane Gay tweet. The main reason to watch the movie is Whitfield - she picks it up on her shoulders and carries it to the finish line.