This book has a good deal of spells written, some with very interesting twists and creative aspects. I've used a couple of them and one of my players also found a few interesting ones. It also has some good explanation of lore and funny notes coming from the most renowned mages of the D&D universe.
However, a great deal of the spells are fillers with sometimes unbalanced or clunky mechanics, as well as reflavoured existing RAW spells. It also sometimes mixes the spellcasting topic of certain classes, especially with those reflavoured spells. Additionally, many spells are so situational, they become hard to include in any build without sacrificing too much.
With a bit of DM veto and help to rearrange the clunkiness, players could definitely use it. But then the other big problem of the book comes along. It's a really big book and it uses the already criticized system of the PHB of having the classes' spell lists in the beggining, and then all the spells are ordered alphabetically, independent of their level. A switch to Spells by level first, alphabetically second, with clarification to what class they belong to in each spell would have been a huge deal better.
To show a couple of examples of what I'm saying:
- Frost Fingers (class conflict): Burning hands but with cold damage. But now clerics have access to it, while RAW they don't have BH.
- Wailing Wind (reflavour, class conflict): Alarm spell, but instead of a ping you feel some wind. Again, now clerics have it.
- Boon of the God (unbalanced): A shorter Regenerate spell, but just as potent for everything but the HP gain. Now 4th lvl instead of 7th level.
- Appraising Touch (situational): Adv to determine price of objects. And it's not even a ritual.
All in all, the book has a great deal of clever spells. But the editing and the fillers make it really hard to find them and I cannot really ask my players to incorporate them because I don't want them to waste that much time. I really wish they had found an easier way to make it more readable.