Faiths of Balance is a great work-horse book. It does exactly what it sets out to do, which is provide information on the *worshippers* of the various morally neutral gods (not good or evil) for players and DM's to use as they will. Additionally it also provides you with various traits, feats, spells, and magic items that you could use in your game. Some of the traits felt a bit copy and pasted, but they are all pretty flavorful so mission accomplished there. The art in the book was very evocative of the various faiths and well done, the writing was the usual paizo quality stuff, and I the spells, feats, and traits were all very useable.
But that's about it. Nothing that opened my eyes and made me say "Wow! That's amazing, I can't wait to use that in game!" FoB is a very useable book, especially if you have a penchant for worshipping the gods inside it, but there isn't anything in here that breaks the bank, mechanically or in the Golarion setting. This isn't a bad thing, but it does stop me from giving a 5 star rating.
I would like to add that there is a section on both the Green Faith (non-deity nature worship) and minor gods as well, so if you'd like more about them check this out.
FINAL WORD: Faiths of Balance is good, but not great. Buy it if you really want more information about worshipping LN, N, or CN gods. Otherwise, just use Gods and Magic or the Inner Sea World Guide.