It's a classic to be sure but the information is hardly current and there are no tasting notes of value, "produces pure highland malt" on and on is not helpful.
For my money, the Whisky Bible still rules - even though I think the marking has started to get out of control. I was sorry to see the SMWS dropped from the latest edition, though.
It depends on what you are looking for. As a historic document, the book is brilliant, with the drawings in it and the descriptions of the late 19:th century distilleries.
If you're into present production and the industrial figures, the book suck... Obviously...
I voted maybe as Bullie said 'The Whisky Distilleries of the United Kingdom' is a wonderful historical document on what was around in the day so if that is what you are after there is no better book but it is no way current so as others say go with Misako Udo's 'The scottish whisky distilleries' A lot of her historical parts are taken from Barnards book but she has really updated the whole experience.
The Misako Udo book surely can't be rated as a classic until the numerous errors are corrected?
A reference book is not entirely fit for purpose (to borrow John Reid's buzz-phrase) if it contains numerous and significant inaccuracies.
Please believe that I'm not being malicious - I truly hope that the errors and misinterpretations are corrected and that the book does become a classic reference work. It certainly has the potential.
For what it's worth, I have enjoyed reading Andrew Jefford's "Peat Smoke..." more than any other whisky book. But it's a totally different type of book from those of Barnard, Udo etc.