I used to be a big fan of lonely planet guides but recently I've found them disappointing and the New Zealand guide is no exception. I gave this book to a friend of mine who has travelled extensively in the country and his overall impression was whilst factually accurate there were some surprising gaps and an overly onerous approach to the logistics of travelling and not enough guide material for the places being visited.
I agree with this description and in fact the same is true of all the lonely planet guides. I suspect this is because they are aimed almost exclusively at the backpacker traveller and less relevant for the modern internet age when guidebooks don't really need to into massive detail regarding how to get to places. When I visit places, I almost exclusively use the internet to make my travel and accomodation arrangements. What I need from a guidebook is lots of portable information about places to visit and sights to see when I get there. In that regard, the Rough Guides do the job much better.