The premise of couple who dislike each other thrown together as bridesmaid and groomsman is common enough, but somehow this one was accomplished nicely. Olivia was somewhat blinded by her own self-interest, but the emotion was legitimate given how it brought back so much memory of her mother. Brian was actually fairly reasonable even if he reacted a little too strongly. But after the setup, their relationship developed nicely and with chemistry between the actors. The resolution for the main couple was obvious and in fact I think it's been done at least once in another TV movie.
I have to remind myself that rom/coms and reality do not fit well together so as ridiculous as the way the bride and groom's troubles developed and solutions approached, I just went with it. The point was that it was a vehicle by the writers to bring Olivia and Brian together.
I liked that the main couple's brunch conversation was fairly real rather than silly or overly invasive. The continuing mix-ups resulting from their peacemaking efforts were mildly funny.