Chess is in a category with West Side Story and Oliver! - quite outstanding musicals by writers who just never delivered again (for different reasons in each case: retirement in the case of Chess; hubris with Bernstein, and drugs'n'booze with Bart). The score is by Benny and Björn who were at the absolute peak of their powers, just before they called it a day: several of the songs are as good as (I would say better than) anything they had come up with in ABBA. And the lyrics are by Tim Rice, also on top form and by then newly-separated from Lloyd Webber. Again, for my money, he was well shot of ALW who struggled to achieve one song per show that could bear comparison with at least half a dozen from Chess. And while it's fair to say the result includes a number of pastiche set-pieces emulating Gilbert & Sullivan, Rogers & Hammerstein and Sondheim (they wipe the floor with him), also included are straight-down-the-line masterworks.
ALW is supposed to be the classically-trained one; but there is more effective classical technique here than anything he ever managed: counterpoint, polyphony, and in Pity The Child, the best modulation you'll ever hear in the rock-pop genre. (Paul McCartney was pretty good at it, but how much he owed to George Martin I'm not sure. The BeeGees were exceptionally good but they threw it off for fun [Chain Reaction]. Pity The Child uses it for awesome emotional effect.) And the outright orchestral pieces are as good as any film music ever written.
So how does the revival do? The critics have been fairly harsh, but if you read them carefully they are really saying they don't like the musical itself, or the SFX. The Murray-Head replacement can be forgiven for his slips, but the ENO Chorus cannot and their evident lack of rehearsal was a bit of a shocker. But the set-piece songs were mostly done very well. Michael Ball is a helluva pro. We give it 8/10 and considered it an evening well-spent. In a week or two it may be even better.
** You can check Gershwin out too for yourself on youtube