Are you sleeping on Duffy's "Endlessly"?

If I'm lucky, it happens once or twice a year. A new album comes out, I listen to it a few times, and I shrug. It's not terrible, but it's not essential either. Then unexpectedly, it grabs me by the ears and refuses to let go. This is how I came to love Lisa Stansfield's Affection, Radiohead's The Bends, and, most recently, Duffy's second album, Endlessly.

Like Amy Winehouse, the artist to whom she is most frequently compared (Dusty Springfield is a close second), Duffy equals Buenos Aires for me. My entire love affair with her and her music is contained in the four-plus years I've been living here. When her debut album, Rockferry, came out in 2008, it was love at first listen. I never really got the Dusty comparisons (there's not even a hint of black in Duffy's voice), but when I listened to her, I was transported back to a time (circa 1965) before I was even born.

Endlessy has been a decidedly more acquired taste. When it came out in early December, it didn't impress me much. Not only was I disappointed by its short running time -- 10 songs lasting a mere 35 minutes -- but why was she collaborating exclusively with Albert Hammond, 66, the guy best known for his '70s cheesy-listening hit "It Never Rains In Southern California," and writing or co-writing a long list of hit ballads, some hot ("The Air That I Breathe," "When I Need You"), some not ("To All the Girls I've Loved Before," "Nothing's Gonna Stop Us Now")? Shouldn't she have worked with someone closer to her own age (26), like Albert Hammond Jr., 30, Hammond's son and rhythm guitarist for the Strokes?

Then one day, after a month with Endlessly in medium rotation, I saw an ad for it on Argentina's Sony TV channel. Its sample track was one called "Lovestruck," and suddenly, I was just that. I'd listened to the album so many times, but how had this sexy, sassy little number gone more or less unnoticed until that moment? Over the next few weeks, I listened to Endlessly endlessly, until it reached that point of undeniable awesomeness when every time I put it on, I discovered a new favorite song.

Where Rockferry, one of my favorite albums of 2008, belonged to the era of beehives and Motown, Endlessly isn't of any one particular time. There are hints of the '60s here and there ("Too Hurt To Dance" is a delicate tearjerker that could have been plucked right from a 1960 Brenda Lee recording session), but when you invite the Roots to be your backing band -- as Duffy and Hammond did on "Well, Well, Well," the first single -- you obviously don't have images of boufant hairdos and the Supremes swirling around in your mind.

There's nothing as immediately infectious as "Mercy," the Rockferry single that made Duffy a rare UK-to-US crossover star, but on "My Boy" and "Keeping My Baby" (today's favorite, which quotes Madonna's "Papa Don't Preach" and shares its subject matter without ripping off the '80s hit), she sounds gutsier, more forceful, no longer a victim of love. A few critics have carped about the occasional pinched vocal on Endlessly, but throughout, Duffy sings with the conviction of star who won't be sized up (or down) as some knock-off talent, a Dusty Springfield manque, or a poor girl's Amy Winehouse.

I'm not saying that Endlessly is better than Rockferry -- or even as good. But it deserves better than it's gotten commercially. The album only managed a No. 9 placing in the UK, and it debuted and (apparently) peaked at No. 72 in the US. It's worldwide sales so far are in the low thousands, where Rockferry topped out at more than six million and was 2008's fourth best-selling album worldwide. That's a steep, potentially fatal plummet for a developing career.

It's probably too late for Endlessly to rebound, not with bigger stars like Kelly Clarkson and Britney Spears due to make their returns any week now. Maybe Duffy was destined to be a one-album wonder. Perhaps she's just too elegant and tasteful to compete with modern pop's top divas. Hopefully, though, when she gets around to making album No. 3, she won't start trying.