Prior to this book's release, I'd been playing in a weekly Sidereals game and enjoying it greatly. When Exalted 2E came out, we embraced the new rules and looked forward to this book with great anticipation. We hoped it would match the quality of the revised core rules, and we were disappointed.
The setting material is good, but it assumes that you're familiar with the 1E book and omits material that players new to the Sidereal Exalted might find useful or necessary. The rules for Sidereal Charms are particularly bad, with many not integrating well with the core rules (particularly with social combat), missing keywords, having confusing or redundant keywords, and so on. We waited for White Wolf's promised errata, but after several months, we ended up rewriting the entire Charm set.
Every argument for and against this book has been made by now. Let me just repeat that my group of longtime Exalted players is still playing Sidereals and still playing by-the-book Exalted...just without this particular book. I would not recommend supporting White Wolf by buying material like this. I'm sure hard work went into this book, and it's a pity that so little of it seems to have made it in the published version.
[2 of 5 Stars!]