The movie is obviously designed as a Jolson vehicle. It is pretty obvious that the star came first, and everything else followed.
Despite being made in 1928, the film holds up remarkably well today, the humour being one aspect that hasn't dated. Jolson sings Sonny Boy to great effect three times, although he puts so much emotion into it that I was left wanting him to sing is straight just once. The film may seem oversentimental but if you engage with this and look at it from the point of view of a contemporary audience you will enjoy it more, and the film's shock ending is, in my opinion one of the bravest I have seen Hollywood do. In fact the only shock endings which I think compare with this are Terry Gilliam's Brazil or Doctor Who: Earthshock.
The supporting performances are sterling, but there's no other actor who has the Charisma of Jolson. It's apparent to me that nowadays, the film's leading lady, Josephine Dunn, playing a singer, would have been given one or two songs to sing, but the producers rightly realised that the audience was there to see Jolson and Jolson alone.
The film is also of historical interest, being one of the first talkies. It's apparent that synchronised sound is used sparingly, and, like its near-contemporary The Jazz Singer, the opening parts use caption slides in place of speech.
Enjoy it for its Jazz age settings, the grand costumes (Miss Dunn's gowns are particularly exquisite) and of course for Jolson's singing.