When I first decided to go to the Lake District and do some walking, this was the book I bought, and I haven't regreted it, and have since bought the second in the series. The walks themselves are well thought out and described, often with information on the area you are passing over. One or two walks have seen or are about to see changes due to path erosion, so it may be time for an updated version.
There are occasionally good suggestions for alternative ways of starting the walks (eg getting the boat from Keswick for the Cat Bells walk) which can be useful, but especially on some of the climbs it doesn't quite make it clear how far up you're going and how quickly; the aforementioned Cat Bells walk has a very stiff (if not that long) climb with some scrambling up rocks at the end that isn't mentioned for example.
Nevertheless, an interesting and generally reliable book with a good selection of walks, info about things you may see on the walk, and backed up with a section of OS Map that means you'd have to go very wrong to get completely lost.