I've been after a thesaurus that's both comprenehensive and easy to use for a long time, and always found the offerings in local bookshops (Roget/Oxford/Collins) to be wanting. For me, this one fits the bill perfectly (okay, ideally I'd like to have its contents online, searchable, etc. but as a book it's hard to see how a thesaurus could be done any better than this).
Here are the key points:
- more than 1.5 million synonyms, according to the introduction, spread over 1361 pages of fairly dense 2-column text, which means it's one to keep by your writing desk, not to carry around in a satchel. Type size is small but readable -- a little smaller than the paperback novel I'm reading at the moment.
- No-frills A-Z layout that makes it easy to find the entry you're looking for (should appeal to those who find Roget overly clunky in use).
- sensible headword choices keep the thing to a manageable size (thus likely look-up candidates such as "thin" and "emaciated" are headwords while the possibly more rarefied "bony" only appears *within* the entries.