A couple more points: First, someone said that they were glad to see that this supplement didn't have powercreep in it, but supplements like this are exactly how powercreep happens. It introduces some new stuff, some of which is a little worse than what came before, and some of which is a little better than what came before. Overall, it's at about the same power level as core, so it looks balanced. Except that's not the way it's actually going to work out: The things that are underpowered, nobody's ever going to take, so they're irrelevant. The things that are more powerful, everyone's going to take, so everyone (or at least, everyone with access to this material) will get a little bit more powerful. Repeat with every new supplement, and eventually you start noticing that everything's a lot more powerful than it used to be.

Second, this confirms something I was worried about as soon as I saw 5th edition: In what directions can it expand? You can always introduce new spells, but there's not nearly as much you can give to mundanes. In 3rd edition, you could at least hope for new prestige classes and feats, but in this edition there are no prestige classes, and feats are somewhere between rare and nonexistent. But spells? Yeah, we're getting plenty of those, and so the already overpowered casters just get even more overpowered.