Billy Mernit's excellent recent blog reminds us that "the primary job of a rom-com writer, is to convince the audience that these two people must become a couple."
There should be such a sense of longing and belonging between these two that we pull for them, & we despair when they're apart.
This is what all rom-com fans are looking for. However, some critics also say that this is what makes rom-coms too predictable.
As Billy says (& I can attest from specs), too many scripts focus on the obstacles, not the couple.
So what to do? I think the secret for a good rom-com (or romantic story line) lies in a proper set up for the inevitable split and reconciliation. If you can properly drive the story toward that split, you can satisfy (maybe) both fans & critics.
What does this mean? Show the main character's world without the love interest. Place the love interest in a position that shakes up the main character's world. The two characters bond, & we see how they are better together than apart.
Then rip them apart to test the strength of that bond, and make them struggle to reconcile, because it's that testing that clarifies to us that these two should be together.
ex. Although not a rom-com, George Clooney's character in Up in the Air does have a well set up romance. The audience sees him alone and satisfied with his no-strings-attached, black-and-white vision.
Then Vera Farmiga's character enters and he suddenly, he sees color for the first time. We're rooting hard for him as he changes in her presence & we're aghast at the split. We root even harder for them.
WHAT I'VE LEARNED: Everything in a rom-com (or romantic story line) should be engineered so that we can see why these two must be together.
Billy Mernit's blog: http://www.livingromcom.typepad.com