I've got a copy of it and it is indeed a classic. However, if you are going to get a copy make sure it has a good contents and index, and that it has many of the more orthodox spellings. Unfortunately, mine is poor on both the above.

As a source, it is nothing special IMO. Gibbon seems to spend more time on creative ways of saying things rather than researching what he is writing about. Some of his conclusions no longer hold water, especially his blaming of the military collapse of the Western Empire on Christianity.

When it comes to post-476BC, I think his usefulness dwindles even more. His own contempt for the Byzantine Empire is apparent throughout his work and severely clouds his judgement.

Having said that, I always found his work highly quotable, much like John Julius Norwich, and it always adds to any piece to have a quotation from the _Decline and Fall of the Roman Empire_