Ron Moody, Shani Wallis, Oliver Reed, and Jack Wild all make up for the weakness of Mark Lester (who is, to be fair, saddled with a lead character who just isn't as interesting as the supporting players). Most of the songs are great, although a couple really aren't ("Where Is Love?" makes my ears bleed), and the 2 1/2 hour runtime flies by.
It's hard to be objective about this film. I grew up with it and seen it over a dozen times. It has a particular resonance for a Londoner like me too. The voices and characters are still out there. The songs are beautiful ( check out John Lucien's superb cover https://www.youtube.com/watch?v=-sbNPKwGDJ4 ) The sets and choreography are great.
Almost a final hurrah for the large scale musical and a handsomely realised production at that, full of splendid musical numbers, rich caricatures and some magnificent sets. Not quite the chocalately confection you might expect with a pleasingly dark undercurrent of murder and danger cutting against the generally jolly vibe. It all works a treat.