Matthew Cole of Slant Magazine, giving the album one and a half stars out of five, said that "after 10 tracks of "Endlessly", I was just begging her to stop", referencing her earlier hit "Mercy". However, some critics were more positive towards the album. Okayplayer noted that the songs "capture a retro American sound reminiscent of sock hops and drive-ins so subtly, that the album could have been called Effortlessly." "Uncut" said that it is "sharp, commercially astute pop music" that is "cool and clever without being contrived." Ann Powers of "The Los Angeles Times" notes that Duffy "tries several different ways to celebrate her unique talents without abandoning the vintage settings that won her such acclaim", calling the lead single a "reggae-tinged rocker" and complementing the return to "Rockferry"-like Northern Soul on tracks like "Too Hurt to Dance." However, she goes on to write that "Duffy has said she wrote the songs in a mere three weeks, and it shows." Many were critical about Duffy's voice on the record. John Bush of Allmusic said that "Duffy's voice [...] has not improved with age, or simply isn't portrayed well here." He goes on to say that it is "clearly not her most potent weapon", criticising her choice to "build an album out of it." Matthew Cole of Slant Magazine said that "the bigger problem with "Endlessly" is that Duffy compensates for her lack of a star persona by overdrawing her syrupy rasp, already noted for its acquired tastiness, into a cartoonish oddity." "Spin" noted that ultimately, it's the vocals that carry "Endlessly". There's no whitewashing of the singer's eccentricities, which feel more pronounced here—she can be gruffly nasal (the oft-repeated chorus of "Well, Well, Well" never stops sounding like "whale, whale, whale") while remaining wholly beguiling." However, Jody Rosen of "Rolling Stone", Melissa Maerz of "Entertainment Weekly" and Will Dean of "The Guardian" were more complementary, with Dean calling it "beautiful" and "sweet" and Rosen applauding it for being "smoky and touched with grit." Ann Powers of "The Los Angeles Times" said that her voice is "delicious to some and cloying to others." Duffy was compared to several female pop singers such as Kylie Minogue, Debbie Harry of Blondie and Madonna.