Brian Wilson, Royal Festival Hall, London<br/>Ghostpoet, Clwb Ifor Bach, Cardiff

The former Beach Boy may be a passenger in his own show, but treasure him while he's still performing &ndash; his fragile genius won't be here for ever

If something terrible should ever happen to Brian Wilson, I have one sincere hope: that his band carries on performing his music without him. The Brian Wilson band are more than mere backing musicians.

They're a magnificent musical unit in their own right, capable not only of replicating The Beach Boys' insanely complex works but also reading the modern-day Wilson's mind and enacting his will. For coaxing one of the true geniuses of the 20th century out of his corner and into theatres and studios, they deserve our gratitude.

That said, their current project, Brian Wilson Reimagines Gershwin, is a strange concept: a band who've absorbed the DNA of artist A (The Beach Boys) performing the music of artist B (the Gershwin brothers) in the style of artist A. Improbably, I'm reminded of Ramones-meets-Abba tribute band Gabba.

Wilson was, he tells us, approached by the Gershwin family to record an album of the works of George (composer) and Ira (lyricist), and given permission to use unfinished fragments of George's music to create two new songs, "The Like in I Love You" and "Nothing but Love". Wilson's new album comprises the first half of his current live show, bookended by an overture and coda based on Rhapsody in Blue, with mind-bendingly nuanced harmonies.

Most of this is familiar even to someone who, like me, has to be dragged kicking and screaming to a musical. Many of the songs are lifted from the opera Porgy and Bess, a problematic work for modern ears. One cannot help flinching as Wilson, a wealthy white man, sings "I Loves You Porgy", an affluent Jew's grotesque parody of the babyish way in which poor black people of the 1930s supposedly spoke. Or is that just me? Actually, it isn't: Duke Ellington and Harry Belafonte criticised Porgy and Bess for its racism.

On the other hand, one could applaud Gershwin for staging a piece with an all-black cast at all in the 1930s. Furthermore, even if I could live without jazz-hands chestnuts such as "I Got Rhythm", there's no arguing with the beautifully languid "Summertime", or the then daringly heretical "It Ain't Necessarily So".

And it doesn't matter that Wilson is a passenger in his own band, often adding little more than fingerclicks, sitting at a keyboard that's seldom touched. It doesn't matter that, when he straps on a bass for "Barbara-Ann", be barely plucks a string. That voice, off-key but with a beautifully broken, yearning quality, is unmistakable from his classic recordings and, during the Beach Boys section, comes into its own.

For the pop-loving atheist, attending a Brian Wilson Beach Boys set is the closest thing to church. This one digs deeper than the obvious hits, giving airings to relative obscurities such as "Salt Lake City", "The Surfer Moon" and "Hey Marcella" (dedicated to "our rival group The Rolling Stones"). But "Wouldn't It Be Nice" brings something hard and immovable up into the gullet, and the full Smile version of "Heroes and Villains", with its nightmarish fairground sounds, terrifies me as much as it did when I was a child.

Wilson introduces "God Only Knows", accurately, as "the best song I've ever written" and, on the line "The world would show nothing to me, so what good would living do me?", gesticulates so wildly he knocks his mic away. After a heartbreaking "Love and Mercy", he waves and walks away. You don't take your eyes off him until he's disappeared. Because you don't quite know if or when Brian Wilson, his band and an audience will get together and do it again.

If the Mercury Prize is a poisoned chalice for previously unknown winners, whither the defeated nominees? Ghostpoet is about to find out. As the album title Peanut Butter Blues & Melancholy Jam suggests, Obaro Ejimiwe deals in home-made beats. At one point he does a DIY echo without an echo effect: "I heard it in a TV programme, so it must be right-right-right ...". All pork pie and National Health, he's a lugubrious presence, a bedroom dub raconteur (literally: one song is about living in spare rooms). He's half Linton Kwesi Johnson, half Daniel Johnston, making outsider music from inside.

Using live guitar and drums, and an Apple laptop that breaks down mid-gig, so we have to applaud his charger, Ejimiwe delivers down-tempo grooves and stoner narratives. A member of Goldie Lookin Chain says hello on the way to the "slow-motion mosh pit", which speaks volumes. The bass on new track "Hampton's House" is so heavy it actually knocks drinks from ledges. Prize or no prize, Ghostpoet, keeping it slow-and-low, will get there in his own good time. Tortoises and hares. Every loser wins.

Next Week:

Simon Price watches Jamaican hotpant enthusiast Rihanna bring Belfast under her umbrella-ella-ella

Rock Choice

Britpop survivors, The Bluetones, play their last ever gig at the Brixton Academy, London (Tue). American neo-goth chanteuse Zola Jesus takes her third album Contatus to Toynbee Studios, London (Mon), and prankster rapper turned lounge pianist Chilly Gonzales begins a residency at the Soho Theatre, London (Wed to 8 Oct).