Taking an educated guess as to what the new No Doubt song—their first in nearly a decade—would sound like, all signs would point to the group jumping onto the Dr. Luke-esque pure-pop bandwagon. They were sort of headed that way anyway with 2002's Rock Steady, an album which eschewed the ska and new wave-influenced alt-rock of their last few album in favor of a more top-40 friendly pop sound (largely courtesy of guest producers like William Orbit and The Neptunes), a direction which lead singer Gwen Stefani of course expanded upon greatly in her solo career.
It seems like a measure of defiance, then, that "Settle Down" just sounds like...a No Doubt song. That's not to say that it sounds phoned-in, or that it doesn't show any kind of musical growth in the years the band's been away, but there's a definite lack of concession to contemporary Top 40 norms going on here—this song could not have been performed by Carly Rae Jepsen, or even 2012-era Madonna. There's no dance beats, no chant-or-fist-pump-along hooks, no featured guests. What there is is a six-minute, dancehall-influenced pop/rock number, with an extended dub outro and the typical No Doubt mix of attitude, vulnerability, hooks, funk and fun. It's a good song, especially for the summer and it would have been just as good a song in the summers of 2002 or 1996.
Gwen seems to anticipate this failure to meet expectations in the song's lyrics, which are borderline-defensive about where she and the band are at right now. "What's your twenty? Where's your brain?" Gwen asks herself in the first few lines, eventually responding with the unequivocal "I'm fine / I'm feeling positive, for real, I'm all good," and concluding in the chorus "But you can see it my eyes, you can read on my lips / I'm trying to get a hold on this / And I really mean it this time."
Really, that's what the song sounds like—like No Doubt being comfortable with who they are and what their place in the musical world is, and not needing to chase any kind of modern pop success for further artistic (or commercial) validation. Perhaps more importantly, it sounds like the song that the band No Doubt wanted to put out—not just Gwen herself, who had become such a solo star in her own right that it wouldn't be surprising to see the group become her backing band, a la Maroon 5 and Adam Levine. It won't get the group a lot of new, young fans, but old-school fans will doubtless be appreciative.