The subtitle of Curry: A Tale of Cooks and Conquerors, by Lizzie Collingham, is more helpful in giving an idea of the contents than the title. Rather than a book about Indian food, it is about India and the British connection with it, told through food. Collingham chooses dishes most familiar to patrons of Indian restaurants in Britain and follows them back to their origins; in the process, she tells much of Anglo-Indian history from the time of the Mughals (17th century) forward. She does include some recipes, both historic and modern, but they don't cover the ground she does in the chapters and the focus stays on the history. The last two chapters aren't even set in India; they follow Indian food as it migrates to Britain and the US, then to the rest of the world. So maybe it is best described as a book on the history of Anglo-Indian food.
Looked at that way, it is a well-told story (assuming you care about either history or food). It is interesting to see how various strands of Indian food (there isn't one national food, there are many) came together in British kitchens to create an Anglo-Indian cuisine - which in some cases degenerated to bland boiled food with a little curry powder thrown in. Curry powder, of course, is profoundly unIndian, since in a true Indian kitchen, the spices will be ground fresh every morning, specifically for the dishes being cooked that day, and they will be added at different points in the cooking to maximize their effect, as she explains well.
Collingham generally does a good job of treating everyone equally (neither the colonizers nor the colonized are patronized), but she slips at one point when she dismisses the British tendency to take Indian flavors and incorporate them into British cooking as complacency. It is the one place she invokes a double standard: earlier in the book, the Indian tendency to take new ingredients introduced by the British and incorporate them into Indian food is a sign of creativity and the resilience of Indian cookery, but when the British do the same, it is complacency.