Part I was tense, funny and tightly focused -- mainly on the odd relation of the two old army buddies, and the indignities each suffered -- one as a native Brit employed by a native twit, the other as an immigrant with great pride and hopes of conquering new worlds finding himself trapped in the tiny prison of the Bangladeshi ghetto. In Part II, Archie and Samad fade into the background, and the script tries to follow four teenagers on their separate paths and really loses focus. I didn't sense such a problem in the book, where of course Zadie Smith could take as much time and space as she needed to develop each of these stories, finally bringing them together into what she herself has called a "calamitous" (artistically) ending. (The TV ending is equally calamitous, a descent into farce that's just not very funny, so they didn't fix that.) Two episodes from the book I especially missed. One is the wonderfully bizarre, horrible failure of Irie's hair experiment -- handled in the TV version in a sadly abridged version. In the novel, it's an operatic tragedy.
In fact, since the producers had to make a choice (or else add another two hours), I'd rather have seen more of Irie and less of Joshua (one of the least convincing characters in either version).
The other thing I missed was the terrible menace, to themselves and to others, of the fanatical Muslim crowd that Millet gets mixed up with. Here they seem merely comical. The burning of Salman Rushdie's Satanic Verses by people who would not sully themselves by actually reading it is an important device in conveying that menace in the novel -- though the name of the book is never mentioned. It is Millet's much grander, socialized response to his father Samad's earlier, personal bonfire of Millet's teenage possessions.
If the TV show gets more people to read the book, it will have done a noble service. And the actors were all wonderful -- especially in Part I.