I love greek mythology, I got into the Percy Jackson and the Olympians series from a young age, and have been reading them for a long time. They got me into greek, roman, norse, egyptian, and other mythologies. I know more about greek mythology than a normal person would. I love that they made a greek-themed book, but it's not really greek mythology. It's a Magic setting crossover book in the disguise of a greek setting handbook in D&D. It's not what I would've wanted if I had asked for a greek-mythology setting. I don't love the push that they're doing to make more M:tG settings. Ravnica came out making a giant-city setting with strange creatures. We already have something like that in D&D, it's called Sigil. This Theros book was released as a pseudo-Greek mythology setting, instead of being true greek mythology.
I guess I would have preferred a true greek mythology setting. I have a connection with Zeus, Hera, Poseidon, Hecate, so on. I know them, they have an importance in our world, and I understand them. I just don't really care about Heliod, Thassa, Purphoros, or any of the gods or characters in this book. It's not true greek mythology. To me, it just kind of feels like it's fake. It's not a genuine attempt to Greek mythology. It's them trying to start a movement for more Magic: the Gathering worlds so they can publish more settings, like people want, but as easy and convenient as possible. To me, by them making more Magic: the Gathering worlds, that's not "expanding the IP of D&D" and more of cheating.
They have the worlds, they can do a bit of work to translate it to a D&D book with new monsters, items, and characters, and the content that they have to make is already laid out for them. It just doesn't feel like they're concerned about making new interesting settings, as much as they are at having the books be as easy to make as possible. I'm not saying it's easy to make a book, because it's not. The world didn't have a map before, they had to make that. They had to make the Satyr and Leonin race. They had to playtest a few subclasses to put in the book so that players would buy it. What I mean is that hard work in products is appreciated by the community. I personally would prefer a brand new greek themed setting, that is truly greek mythology, opposed to grabbing the thing they have closest to that theme, and making a book out of it.
The book is very well written, I love the Satyr, the Eloquence Bard, the magic items, mythic monsters, the nymphs, and the piety system is very cool. The book has good content, talented people contributed to it, but it still just feels to me that they did Theros because it was smoother sailing than making a unique world, or revamping an old world.