Since Gnarls Barkley jumped into everyone's consciousness on the back of a single called "Crazy", would you forgive me the groaning joke if I said their follow-up sounded a little like someone prescribed mood stabilizers? That's the gripe you'll probably hear from most people: The Odd Couple is flatter, in both directions. The joy of this duo's debut was a kind of erratic, anything-goes lightning-bottling; its chintzy, slapdash qualities were more than made up for by the number of bottles containing honest-to-god scraps of actual lightning. Hit the big time on the strength of one of those, though, and the world has big-time demands. It was inevitable that these two would have to fight past their idiosyncrasies (producer Danger Mouse's short attention span, singer Cee-Lo's ease with throwing vocals together on the fly) and deliver something more focused, something that doesn't require so much sorting through. They've done that, to an extent-- not by any huge, transformative leap, but a little. And much like your average SSRI, it means less of the unpredictable magic and the sideways song-notions that sold the first album.

It'd be cruel and point-missing to pick on them for this-- as cruel as it'd be to tell your friends they're more "fun" when they're off their meds. More importantly, there are times, as DM's beats trail by in their muddy, tasteful way, where Cee-Lo sets to work developing something terrific, even if it's not the shiny pop thrill a lot of fans might want. What Cee-Lo seems to be after is a kind of restrained, gut-searching soul music, packed with even more self-doubt and self-laceration than the first record. Get over the lack of colorful pop baubles, and you'll notice that the best work here comes in the form of low-key cuts about isolation and uncertainty, like "Who's Gonna Save My Soul". Oddly enough, that means this album will be a grower-- dead opposite the flash and fade of that debut.

Danger Mouse, meanwhile, is tackling a different set of challenges. Somewhere between Outkast's "Hey Ya" and this group's "Crazy", the formula for success with this stuff became clear: Make hip-hop-styled music based around the sound of the 1960s-- the old soul music that's a common ancestor to nearly everything going today-- and you'll bring in fans from every direction. DM's taken that to heart here, and he keeps his beats warm and organic, with none of the futurism that came through on St. Elsewhere, and plenty of straight-up 60s grooves: "Surprise" drops in a vocal harmony that may well be sampled from the 5th Dimension, "Going On" works its organ and hand-claps, and "Charity Case" even has Cee-Lo recreating the ooh-aah backing vocals from Sam Cooke's "Chain Gang". Where the last album covered a 60s-styled track from the Violent Femmes, this one has Gnarls writing what might as well be one-- a great bratty thing called "Whatever", filled with half-mocking sympathy for the teenage loser pining for girls and yelling at his mom.

But it's not always in the way you'd think; most of DM's warm, organic vibes here are dark, slow-creeping, blunted, psychedelic ones, and they don't stop him from trending left-field. (The shaky syncopations and grotty sound of "Open Book" could have come straight from Tricky.) In the end, that leaves the bouncy pop tracks here seeming like the odd ones out: This album might be more focused than its predecessor, but what it's focused on is a the kind of murky, paranoid weight and depth that doesn't much make for chart-climbing singles. Gnarls Barkley's combination-- an r&b singer and an "underground" hip-hop producer (roughly)-- isn't so much of a novelty these days; it's essentially the same thing you'd get from Erykah Badu's newest album, a pretty apt peer for The Odd Couple. Listen to this album in that context, and you'll be a lot more likely to hear the progress they're making. The next pressing question, besides what we can do to help Cee-Lo cheer up, is this: If this is the album where we watch patiently as this duo develops its third dimension, what are the chances that these two guys-- who, unlike the average rock band, have plenty of other projects they could be off working on-- stick around to show us what their "maturity" might look like?