I should state up front that I know next to nothing about the real-world history of Indian arms and armor, so my evaluation of this book rests entirely on its usefulness as a gameplay aid, without respect to historical accuracy or inaccuracy. As a gameplay aid, parts of it succeed brilliantly, and parts of it succeed with less glamour. Overall, this product effectively provides D&D 4e players and DMs with tools to impart the flavor of the Indian subcontinent to a fantasy campaign.
Chapter 3, on Indian weapons, is hands-down the most exciting part of the book. If you want to recapture the feel of your AD&D monk wielding bagh nakh, a punching dagger, or a kukhri, you'll love this chapter. The supplement provides not only statistics for over two dozen new weapons—including, be forewarned, firearms, which I would introduce only with great caution—but also plenty of flavor text, illustrations, and feats for use with those weapons, plus a nice review of the Indian cultural variations on standard D&D weapons such as swords, axes, and the like.
I was less taken with chapters 1 and 2, on armor and shields, respectively. Here there seemed to be less variation from the standard D&D equipment, which made the chapters somewhat less interesting. These two chapters are over by page 15 of a 64-page book, suggesting that my reaction is not entirely subjective and idiosyncratic. Do, however, pay special attention to the innovative ways in which materials various materials compensated for the unavailability of leather due to religious taboos.
My current D&D campaign takes place in a fantasy version of Earth, and the PCs are Europeans traveling in Oceania and Southeast Asia. They're very likely to travel to Hridayaja—my campaign world's version of India—before the campaign is through. When they do, I'll definitely turn to this book to season the NPCs appropriately. If I were running an entire campaign set in an environment like Southeast Asia, I would want each of the players at my table to own a copy of this supplement. I could wish for some nicer layout and fewer stray hyphens, along with some other stylistic niceties, but I expect to find this supplement quite helpful in the months to come.