Given the size of India, and the sheer number of things to do see and smell, a book that covers the entire country will always have to make compromises, but LP have done a good job with this guide.
This is a BIG book, so it is not really necessary unless you intend to travel widely across the country. Regional guides would be a lot better for just the north or south.
I did however, find this book to be very useful. I Also saw the Rough guide a lot. Whilst I thought that the RG was a far more detailed and stimulating read in terms of history and background, the LP won when it came to listings, maps and transport connections- which in India are far more useful in the road. Also, the RG has gone a bit upmarket, which is great for some, but this has left few budget options. The LP however always gives good cheap loging and eating.
Creating a detailed guide for all India would result in a 12 volume encyclopedia, even condensed, this guide looks like War and Peace. Inevitably this results in many off the beaten track places being left out, the section on NE India for instance is a bit rubbish. Some extra explanations would be nice (the blurb on the Taj Mahal is tiny) But on the whole, this is a good guide.
Overall, a good crack at a hard job, but would not suit short term travellers.