Motown the Musical (Shaftesbury Theatre)

Will Berry Gordy, founder of Motown in Detroit in 1959, go to his own 25th anniversary concert in 1984? Will Diana Ross survive without the other two Supremes? Will Berry and Diana get it on together after a disappointing night in the sack in Paris?

These and other questions – why does Smokey Robinson look like Lionel Richie? Why does a race riot become an anti-Vietnam war protest and a tuneless parody of Hair? – flit across an evening then flops in an untidy heap between snatches of Motown classics served up with punch, pizazz and some fairly obvious backtracking enhancement.

Of course, if you're going to the theatre for a party or a karaoke evening – at my press preview, Kenny from Brentwood and Eleanor from Fife, both in horrid jumpers, joined Diana Ross in Las Vegas to give us their versions of "Reach Out and Touch" – you will be cheering all the way through and standing at the end.

But you won't be seeing anything half as classy as Jersey Boys, Beautiful – The Carole King Musical or Sunny Afternoon, all of which modestly aspiring back-catalogue shows knitted songs and story with wit, propulsion and clarity.

Motown The Musical comes across as a muddled vanity exercise by Mr Gordy, still going strong at 86, and here credited as lead producer and librettist. He's the star of his own show, fulfilling a dream of "wanting to make people happy" just like his boyhood hero, Joe Louis, who whipped Joe Schmeling and won the world heavyweight title.

There's even coy reference to maybe, one day, making it all the way to the West End! That's after a lot of location switches starting in his trophy room (photos and gold discs) while sulking about not going to the concert – people he nurtured signing rival contracts, bad blood after years of intimacy, and so on – with over-familiar film inserts (Martin Luther King, Angela Davis, Nixon and Robert Kennedy, Walter Cronkite announcing JFK's demise, etc) playing footsie with ideas of black power in a white man's pop industry.

The show takes off sporadically with set pieces by The Temptations and Four Tops, Martha and the Vandellas, old Smokey (Charl Brown), Stevie Wonder (Jordan Shaw) the Jackson Five led by terrific little Eshan Gopal as Michael and majestic Keisha Amponsa Banson singing some of "My Guy." But Lucy St Louis is harsh and pinched, in manner and voice, as Diana Ross, though she improves as the show goes on, and on.

Motown evolved as a formulaic, medicated sound through gospel, rhythm and blues and a syrupy, irresistible melodic twist, and Gordy, along with old Smokey, wrote many of the greatest songs. But the definition of the artistry, and the recording studio aesthetic, is never as well established as Gordy's own fight to create the phenomenon in the first place, using saving funds from the family's grocery store business and setting up shop in the house he dubbed "Hitsville USA."

The first act of Charles Randolph-Wright's production doesn't know where, or how, to end, and the second act flounders around a big bust-up between Gordy and Marvin Gaye (Sifiso Mazibuko) before subsiding in wide-grin sentimentality at the concert. Some of the costumes by Esosa I liked, especially the shiny satin suits and flared skirts, and the sixteen-piece band under Gareth Weedon's musical direction is chilli-pepper hot.

Best of all, Cedric Neal as Gordy has a truly remarkable voice and sings up a storm from start to finish, though the song with which he raises the roof, "Can I Close the Door," before drowning in a puddle of oh-my-gosh gloop, is pretty awful, and nothing at all like Motown. No worries, though; we've still got "Ain't No Mountain High Enough" and "Dancing in the Street" to come and yes, that is a cue for you all to get up and guess what…

Motown The Musical runs at the Shaftesbury Theatre until 18 February 2017.