Unlike The Elements of Harmony, which it shares its overall design with, this is an in-universe book, written from an in-universe perspective. You won't find anything about the show here; you'll find material from the show, presented in written form. In fact, the book itself is intended to be a real-life edition of the journal that Luna and Celestia kept on the show and that the Mane Six continued writing in throughout S4.
All that I knew, and expected, and indeed looked forward to.
Truth to be told, though, the book's not as good as I'd hoped. It's not a bad book, certainly not, but it's very clearly aimed at children, and this affects both its content and style. The first half of the book, the part written from Celestia's and Luna's perspective, is where this is the most prominent. The sisters are younger and understandably less experienced; yet by their own admission they're also still older than most non-alicorns, so I was dismayed that they often sounded like modern-day teenagers rather than Equestrian princesses. And the adventures they embarked on and the issues they faced lack the depth that has made the show so refreshing; doubly annoying given that already MLP:FiM has already proven that "for children" does not have to mean this.
This isn't to say this part was all bad; there were some interesting origin stories, including the creation of the castle in the Everfree, the first time ponies meet zebras, and more. Star Swirl figured prominently as Celestia's and Luna's tutor as well.
The second half of the book, where the Mane Six write about their own adventures, is a bit better — I chalked this up to it having the show itself to prop it up, the episodes of S4 dictating (in rough terms) what they'd be writing about, and the ponies' characters already having been firmly established. That said, it still didn't quite reach the quality of the show itself.
And that's surprising, really, given that the book is actually written by Amy Keating Rogers, who's also a writer on the show and has quite a few episodes under her proverbial belt, from S1E3 to S4E21. I can only imagine that the higher-ups at Hasbro wanted to have a "childish" book, but why? The huge success that MLP:FiM has seen is due to it not just appealing to kids, after all. And would the kids have minded if the book was a little more like the series it's based on? I don't think so.
Either way, if you've not got this book yet... I'm not recommending against it, but I'm also not recommending for it. Again, it's not a bad book, but neither is it a must-have.