I must say I do enjoy this one quite a lot. Some of the pros/cons of The Midnight Mirror:
-Good opening scene to establish the mood in Karpad. DM should probably play it up a bit more as the PC's investigate, but a lynching is something that stays in people's head. Would have been nice if there was a concrete way for the PC's to learn about the fetchling uprising, but it is something they'll probably ask of their own accord.
-No new monster, but we do have a new disease, Wondrous Item and Minor Artifacts that could be great plothooks for future adventures.
-Investigation section is just about right for this PC level. It flows well, with no need for the DM to fill in gaps that I could spot.
-NPC's have decent characterization. Might need to improvise a bit for some, but a decent DM shouldn't have any trouble.
-Stats for Stepan would have been nice, especially if the PC's decide to fight him. I would personally give him a level of cavalier, but that's just me.
-Good dungeon with 2 great boss fights. Very good descriptions, very thematic, and good encounters all around. Throwing in a haunt wouldn't be amiss, but I am be perfectly happy with The House of Night as it is.
Just take my money Paizo, its yours. Just take it all.
Absolutely loved this book. The fluff on the four Horseman is great, the new daemons are fantastic (if a bit high on the CR scale), the description of Abbadon is dark and ominous without being GRIMDARK, and the Soul Drink class is very flavorful.
Only minor complaints I have are the concentration of daemons at the high CR's and a couple spelling inconsistencies. Outside of that though, this is a very good book. Its nice to see the Neutral Evil fiends fleshed out as well as the devils and demons, you just don't get this in D&D.
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.