I've had this book about a month now and I'm only half way through it - not because it's heavy going but because there is so much information crammed in to it, I keep going away and looking up references for further reading on particular areas of interest to me (which means pretty much all of it). That is another thing this book is extremely well referenced so if there is a particular area you want to read more on, be it evolution of bats, echolocation, flight and flight dynamics etc etc etc there are some absolutely brilliant references in the reference list - for those not in an academic institution Google is your friend when it comes to tracking down references!
The book itself is an updated version of an earlier one by the same author, there have been a lot of advances (research moves forward) and he has taken the time to include these as well as adding a chapter/more on the conversation of bats.
This book is fantastic, as someone with a degree in zoology I knew all about flight in animals, but my degree was a few years ago now and the treatment that Altringham gives to the issue of flight is amazing. He takes it right back to first principles of an aerofoil and builds on that, though if you want to skip the equations and the like then the chapter on flight is still very readable.
This book spans and bridges from hobbyist/armature ecologists through professional ecologist to those conducting cutting edge research on bats. Yes it seriously is that good in the way the author has written it, you might not realise it but on finishing reading this book, whilst it wont make you an expert, many years of fieldwork and research is required for that in any subject, it will fill you with a huge amount of knowledge on bats and their ecology and make you a touch point for those around you wanting to know a little more. You will also, I'm sure find yourself going back to re-read certain areas and even look up some of the references.
If you are looking for a book that tells you about the evolution and the ecology of bats, giving them a world wide treatment then get this book. If you are just looking for a field guide to British bats then, I would not recommend it for that, but would say buy it anyway as you're already interested in the real stars of the night!