In the decade since it emerged from Bellingham, Wash., Death Cab for Cutie has risen from indie-rock buzz band to darling of a prime-time rich-kids soap opera to debuting at No. 1 on the Billboard albums chart with its recently issued seventh album — still music’s most impressive testament to mainstream popularity, even in the era of the digital download. Despite this success, plenty of listeners have always agreed with the criticism that Summer (Rachel Bilson) made of the band on “The O.C.”: “It’s like one guitar and a whole lot of complaining.”

Yes, the group has always had two guitars, and sure, that’s slighting both the lyrical complexity of bandleader and tenor vocalist Ben Gibbard and the musical ambition of producer and lead guitarist Chris Walla during their best moments, especially “Transatlanticism” (2003). But you can certainly understand how the band could come across as unbearably earnest and painfully heartfelt, either in concert or on lesser efforts such as its last release “Plans” (2005).

Lyrically, Gibbard steps outside himself much more on “Narrow Stairs,” adopting different roles in gripping songs such as “I Will Possess Your Heart,” a gorgeously seductive piano ballad written from the beyond-creepy perspective of a stalker, and “Cath,” an empathetic portrait of a women who knows her pending marriage is doomed, but who can’t summon the courage to change course; “She holds her smile like someone would hold a crying child,” Gibbard sings. Meanwhile, the band stretches out musically far beyond the mid-tempo jangle that has characterized so much of its work, exploring the more dramatic and textured art-rock soundscapes of mid-period “Radiohead” or Wilco circa “Yankee Hotel Foxtrot.”

Death Cab for Cutie hasn’t entirely abandoned its tendency toward mopey melodrama; witness “Your New Twin Bed” and “Pity and Fear.” But “Narrow Stairs” is strong enough to convert most skeptics, Summer included.