What do we want in travel guides? I believe we want accuracy and a balance between context (history, literature, architecture, culture, etc...) and pragmatics (timetables, addresses, prices, etc...). This guide to India is the best of the lot, conforming to my simple formula.
It's nice and thick, to give the cultural traveler enough to contemplate, but it's also portable and durable, to fit the needs of the frustrated backpacker. Footprint has been at India for a long time (this is the 18th edition!), so you can expect a well-refined and useful product, not to mention an enjoyable armchair read. The book is as useful in the Indian countryside as in the cities. It's really THAT comprehensive, and it includes detailed chapters on Kashmir and other Himalayan provinces.
Don't buy this book looking for pretty color photographs or graphics. You'll need your mind to create those. And when you go to India, you'll get to test you visual imagery against reality. It's really quite exhilarating!
As a fan of Rough Guides, this is one of the few that I will recommend ABOVE that excellent series.
If you haven't been to glorious India, buy this book and go... alone if necessary. I've been four times, always with this book. It has NEVER let me down.