As with all the gazetteers, the Five Shires is very in-depth, adding whole swathes of background detail to Mystara. Of special note is that this was written entirely by Ed Greenwood, and I haven't come across much non-FR material by him over the years.
It shines a different light on halflings, certainly giving them an identity beyond Tolkien's 'farmers and scouts' stereotype. But overall its value depends on whether you're interested in developing or using the Hin a great deal.
Reasonable scan considering its age. Basic chapter bookmarks included.