The musical relationship between Nancy Sinatra and become has become a blueprint for the male and female song, Mark Lanagen and Isobel Campbel have managed to get three albums out of basing their sound on them.

Campbell and Lanegan, enjoying breakfast after stealing Sinatra and Hazelwood's sound.
At their most moderate, Hazelwood and Sinatra cover the classic songs well; Their cover of 'Jackson' manages to walk the line of sounding a bit like the 'Only Fools and Horses' theme tune, while still being good; their version of 'You've Lost That Loving Feeling' is better than any version I've heard. Lee's gravelly world weary defeated yet defiant voice grumbling under Nancy's sweeter bird song voice.
But it is Hazelwood's own songs where they really shine. Hazelwood takes on the guise of the dark stranger attempting to seduce and deflower Sinatra. Some Velvet Morning' is a lolita-esque tale of a man's desire to take the virginity. In the song, Sinatra is called Phaedra, while she unlikely to be the same Phaedra that fell in love with her stepson, merely by invoking her the song places a darker twist on the song. Phaedra is best known in Greek Mythology for falling in love with her chaste stepson Hippolytus, when he rejected her advances she accused him of rape culminating in his death, after being cursed by his father Theseus. Overcome with guilt, Phaedra committed suicide, leaving Theseus without a son or a wife. In this context, the song takes takes on an incestuous undertone, with the generation gap already present in the track with Hazelwood, a slave to his own desire playing off against the innate beauty and innocence of Sinatra.

The relationship between Nancy and Lee was actually a professional one, although Sinatra admitted she was attracted to him; Hazelwood was recently married and had two young children when their relationship began. the sexual tension oozes through the songs they preformed together. Summer Wine is another highlight of the 'Nancy and Lee' album where this time, Nancy does the seducing, sharing her strawberry and cherry wine with a dark stranger before leaving him in the morning craving more of her 'summer wine' I reckon the song is all to do with metaphors, when artists talk about fruit, it's usually got something to do with fertility and sensuality (sweet tastes, ripeness etc)
Whereas Hazelwood is feels that he has found paradise, Sinatra looks at the encounter more casually, asking him to 'help her pass the time.' later in the song it becomes apparent that she saw the whole incident as a transaction, she gave him her 'summer wine' and in exchange she took his 'silver spurs a dollar and a dime.' Summer Wine is a nice twist on Some Velvet Morning.

Kate Moss and Primal Scream covered Some Velvet Morning.
Beyond the sexual tension and interesting juxtaposition between his and her voice, the orchestration is lush, large and effortlessly dances over the borders of easy listening, country and 60s psychedelia. Hazelwood was a disciple of Legendary gun totting porn actress murdering genius/all round good egg Phil Spector, and it shows. The reversed guitar solo on 'Sand' the cut and paste sound on Some Velvet Morning and the general big 'Wall of Sound' that litters the 'Lee and Nancy' album.
Lee died in 2007 but Nancy is still releasing music, although she has spent her career eclipsed by her father, ol' blue eyes. The best thing in my opinion to come from the Sinatra family musically wasn't the poncey skinny italian as well known for his suits and his mafia friends as his penchant for sleepwalking through songs. I would take Nancy and Lee's output over pretty much anything he ever did.
Listen for yourself.