Sorry, but I have to disagree with the previous review. I found Neil Wilson's Edinburgh City Guide extremely helpful. It provides a good mixture of historical background information on 'sights', and recommendations for 'eating', 'drinking' and 'sleeping'. And, yes, it does mention the Royal Botanical Gardens -- at least in the 4th edition of 2006 (although they are somewhat hidden in the index: you have to look under 'parks and gardens').
Particularly the maps on the last few pages were a great help. They are detailed and accurate (as maps should be) and made navigating the city easy. The book even mentiones the fact that there is now a regular bus service to the airport (no 35), a fact the tourist information at first denied.
Obviously, there are more extensive guides to Edinburgh, and the 226 pages don't come exactly cheap. But on the whole the book is worth its money, and its compact size makes it an ideal companion on a walking tour through Edinburgh.