If Amadou and Mariam’s last album felt like a shift in the couple’s career then Welcome to Mali feels like an even greater one. Someone who was disappointed by Dimanche à Bamako might have consoled herself by thinking that the album was a one-off, an aberration, a fling with Manu Chao that didn’t need to be repeated. “They’ll be back to normal after this,” that person might have said. “No more Chao, no more experiments.”

Then Welcome to Mali arrives and the person is stricken with horror. She writes angry letters to Nonesuch. She makes funeral pyres out of Wati. She tears her hair. She weeps. Her idols have collaborated madly again. Not with one person this time, but two, three, four, five. Damon Albarn! Rappers! The old Amadou and Mariam songcraft is there, but nearly everything on top of it is different. She decides that Dimanche à Bamako was not so bad after all. “At least there they only went in one new direction,” she says. “Here they change all the time.”

And I think: Well, why not? Let them change.

Which invites the retort: Fine, but why should we pay for it?

Welcome to Mali is something more than an experiment, and something less than a fully satisfying and coherent album. It has strengths and weaknesses. It is not entirely strong and not entirely weak. It is not entirely anything. The strength, as always, lies in the couple’s songwriting aptitude. If there is such a thing as a catchy-melody gene, then they were both born with it. They’ve been husband and wife for decades, their children are grown, but as soon as they stand in front of a microphone, then they’re young, happy, married just this afternoon, and fizzy with love. That hasn’t changed.

The opening song, “Sabali”, is the one they made with Albarn. Mariam sings, “Sabali, sabali”, her voice squeezed artificially up to a bat-squeak register, while a keyboard rolls and a drum machine goes pat-a-pat. Here are their trademarks: the melody that is simple yet affecting, the lyrics that are heartfelt yet banal, the mixture so apparently natural and unmeditated that it teeters on the brink of being too basic, too much like a nursery rhyme. “Sabali” had the effect on me of a super-sour sweet: pleasurable without being pleasant, a taste that I want to keep putting in my mouth even though I can’t quite explain why I want it there.

The album goes on. There are love songs. Amadou sings one of them in English, which turns out to be a mistake since banalities sound handsomer in French, the Malians’ default European language and the one they usually use in their lyrics. The kindest thing you can say about this is that he’s not alone. When the Canadian-Somalian rapper K’naan arrives to guest star on “Africa”, he invites Africa to go “up and down and round and round” until he stops sounding like a man paying tribute to a continent he loves and starts sounding like a grubby drunk trying to glom onto the nearest waitress before she throws him out.

We’re better off with the shuffling funk jog of “Djuru”, the trumpet-swing of “Compagnon de la Vie”, and with “Bozos”, in which the dry rasp of a ritti matches the same noise in the couple’s voices. The piano and violin that arrive during Amadou’s English-language song are awkward but interesting. This track is not the right place for them, but there’s no reason why this dabble with classical Western music shouldn’t be pushed farther in the future. The same goes for a lot of the things on Welcome to Mali. The album has the feel of a toe being dipped in the water.

Back in the 1990s, Amadou & Mariam launched themselves on a course of solid Mali-blues, pushing new things with each album, eventually planting themselves firmly and plateauing in goodness. Now they seem to be looking for ways to incorporate Western electronic pop—not the very mainstream, thrusting kind, but the offbeat sort that bubbles around the edges of things and attracts loving audiences on blogs runs by people who pride themselves on their ability to discover the unexpected. In the future, Welcome to Mali might look to us the way their 1998 Sou Ni Tile does now: A step on a journey, but not the end of it.

• Multiple songs MySpace