A rock & roll open secret: U2 care very much about what other people say about them.

Ever since they hit the big time in 1987 with The Joshua Tree, every album is a response to the last -- rather, a response to the response, a way to correct the mistakes of the last album: Achtung Baby erased the roots rock experiment Rattle and Hum, All That You Can't Leave Behind straightened out the fumbling Pop, and 2009's No Line on the Horizon is a riposte to the suggestion they played it too safe on 2004's How to Dismantle an Atomic Bomb.

After recording two new cuts with Rick Rubin for the '06 compilation U218 and flirting with will.i.am, U2 reunited with Brian Eno and Daniel Lanois (here billed as "Danny" for some reason), who not only produced The Joshua Tree but pointed the group toward aural architecture on The Unforgettable Fire.

Much like All That You Can't and Atomic Bomb, which were largely recorded with their first producer, Steve Lillywhite, this is a return to the familiar for U2, but where their Lillywhite LPs are characterized by muscle, the Eno/Lanois records are where the band take risks, and so it is here that U2 attempts to recapture that spacy, mysterious atmosphere of The Unforgettable Fire and then take it further.

Contrary to the suggestion of the clanking, sputtering first single "Get on Your Boots" -- its riffs and "Pump It Up" chant sounding like a cheap mashup stitched together in GarageBand -- this isn't a garish, gaudy electro-dalliance in the vein of Pop.

Apart from a stilted middle section -- "Boots," the hamfisted white-boy funk "Stand Up Comedy," and the not-nearly-as-bad-as-its-title anthem "I'll Go Crazy if I Don't Go Crazy Tonight"; tellingly, the only three songs here to not bear co-writing credits from Eno and Lanois -- No Line on the Horizon is all austere grey tones and midtempo meditation.

It's a record that yearns to be intimate but U2 don't do intimate, they only do majestic, or as Bono sings on one of the albums best tracks, they do "Magnificent." Here, as on "No Line on the Horizon" and "Breathe," U2 strike that unmistakable blend of soaring, widescreen sonics and unflinching openhearted emotion that's been their trademark, turning the intimate into something hauntingly universal.

These songs resonate deeper and longer than anything on Atomic Bomb, their grandeur almost seeming effortless.

It's the rest of the record that illustrates how difficult it is to sound so magnificent.

With the exception of that strained middle triptych, the rest of the album is in the vein of "No Line on the Horizon", "Magnificent" and "Breathe," only quieter and unfocused, with its ideas drifting instead of gelling.

Too often, the album whispers in a murmur so quiet it's quite easy to ignore -- "White as Snow," an adaptation of a traditional folk tune, and "Cedars of Lebanon," its verses not much more than a recitation, simmer so slowly they seem to evaporate -- but at least these poorly defined subtleties sustain the hazily melancholy mood of No Line on the Horizon.

When U2, Eno, and Lanois push too hard -- the ill-begotten techno-speak overload of "Unknown Caller," the sound sculpture of "Fez-Being Born" -- the ideas collapse like a pyramid of cards, the confusion amplifying the aimless stretches of the album, turning it into a murky muddle.

Upon first listen, No Line on the Horizon seems as if it would be a classic grower, an album that makes sense with repeated spins, but that repetition only makes the album more elusive, revealing not that U2 went into the studio with a dense, complicated blueprint, but rather, they had no plan at all.