What makes a good film noir romance? And how is it different from, say, a romantic comedy or romantic drama?

A romance in any genre surely must have plenty of trouble and complications to create enough tension to captivate audiences.

The difference in classic film noir lies partially in the universe which the characters inhabit. Whether it's a seedy dive bar, a stuffy New York apartment, or a fancy house on Russian Hill, the noir ambiance pervades.

But film noir lovers are different too. They're not just two schmucks in love trying to make it work.

Instead, our protagonist is usually overcome with an obsessive and/or fatalistic desire. And, it's usually the male (except in Joan Crawford movies), who is the one haunted and driven.

And that's why the femme fatale is so prevalent in noir. She may be consciously or unconsciously seducing him into her web for her own desperate needs or she may be merely using him to further her own position in an underground world of crime. She often "belongs" to some more powerful, even evil kingpin.

Problem is, she usually falls for the very guy she set out to use and then the two of them are really in trouble. So, either she follows her heart and goes with the ever-suffering protagonist, thus incurring some form of mortal or legal danger for both of them, or she nobly sacrifices her own happiness to save her beloved.

Either way, it generally doesn't end well. But oh, how we love identifying with those fierce passions run amuck.

Other variations of the classic film noir love triangle involve a real sweet girl or wife, our male protagonist and the femme fatale.

Another common characteristic of film noir lovers is that our main guy knows he's going down, but just can't help himself. One or both of the lovers may be headed towards self-destruction, yet feels powerless or lacks the will to stop it.

Why are we so fascinated with film noir romances? Perhaps it's the irresistible fatalism these characters are caught up in, where the fragile promise of desire consummated is supplanted by an inner torment taken to the nth degree.

And for our voyeuristic pleasure, here are five examples of some favorite doomed-from-the-start film noir love affairs:

1. Johnny (Glenn Ford) and Gilda (Rita Hayworth) in "Gilda" (1946). The pain is palpable in this complex love triangle. Johnny's best friend and boss is Ballin (George MacCready), a man whose new bride happens to be Johnny's ex flame. He can't bear the way she treats his friend, but is also tormented by his own rekindled attraction to her and vice versa.

2. Mae Doyle (Barbara Stanwyk) and Earl (Robert Ryan) in "Clash By Night" (1952). Mae Doyle tires of her new nice- guy husband and goes after his dark and moody friend Earl. They embark on a torrid, unhappy affair.

3. Mark (Dana Andrews) and Laura (Gene Tierney) in "Laura" (1944). Quietly intense detective Mark McPherson falls hard for the beautiful woman in a portrait who is supposedly dead. His obsession grows as he investigates her things and the men in her life.

4. Helen (Claire Trevor) and Sam (Lawrence Tierney) in "Born to Kill" (1947). He's a killer and she knows it, but Helen and Sam are fiercely attracted. She tries to avoid him since she's already engaged, so he goes after her rich sister instead. This only incites their passion and things get lethal.

5. Jeff (Glenn Ford again) and Vicki (Gloria Graham) in "Human Desire" (1954). Jeff's the nice-guy train engineer who gets sucked into murder and mayhem by the irrepressible Vicki, whose husband Carl (Broderick Crawford) is obsessed with jealousy and suspicion.

As these films illustrate, a film noir "romance" is rarely a just a sweet love affair which happens to be set in a dark alley. Rather, it's usually a desperate attraction between two otherwise alienated souls who find a rare kinship in one another. But due to circumstances of their noir universe (whether external or internal), it seems their union can only lead to destruction, whether to themselves or to others.