I have always been a fan of the Lonely Planet books, having recently used the Lonely Planet Iceland and Greenland book to great effect. I like this London guide because it is a nice size (easy to carry) and is full of genuinely useful information.
I particularly like the very detailed maps in the back of the book (there are 16 color maps in addition to the tube map and a few other handy things back there). The maps make planning itineraries much easier than if they are spread throughout the book. One minor quibble about the maps, though: the maps are of excellent detail, but cover relatively small geographic areas. That's ideal for detail, except for the fact that there is very little orienting information about how the various maps fit together. It's not a huge deal, but is the only real room for improvement that I saw in the book.
As far as information goes, the hotel and restaurant stuff is pretty standard fare, but the information on sights and attractions is wonderful. I am especially fond of the "Highlights and Lowlights" sections which point out the things generally of highest import to a tourist. Of course, there is substantial information on other things, but this 'do not miss' feature is great. I was also especially pleased with the detailed public transport information including the tube, trains, taxis, buses, and all five airports (and how to get to and from them.)
In short, I am really impressed with this latest edition of the Lonely Planet London book, and will definitely be packing it when I go to England next.