I read this on a lark after learning of its existence as it passed through the library. As often happens when rating things, two stars seems a bit harsh, but the linked phrase "it was ok" matches my feelings perfectly. The Spiderwick Chronicles series is fun enough, but I always felt the main highlight for it was Tony DiTerlizzi's art. His art that is featured in this book is recycled from other works, and it is mixed with a bunch of other art which either mimics a found-object/scapbook style, is just bad, or both. And it's not like the "lore" of the Spiderwick family or the setting is really all that interesting in the first place.
I imagine it would be a fun book for someone who really, really loves the series, but otherwise not really worth it in my opinion.