I have the PDF, I guess I just feel about 180 degrees different than you (so far). The adventure didn't interest me at first glance and after reading through the "review" I linked too it just seems like a terrible railroad later on.
I don't know what to do with this book, yet I immediately made use of Eberron and Ravnica (I don't have Wildemount). At first glance the only thing I am interested in taking for my game is the idea of epic destinies. However, I still need to read up on them to see if the implementation matches my imagination. So far, most of the rest of this book has not.
Not sure about character creation options (we have the same characters since we started with 5e 5 years ago), but some of the races and subclasses do sound interesting - but as the DM I don't worry about that stuff much and leave it to my players (so that doesn't really affect my interest level). We have way more character options than we will ever use, so that is not a big selling point for me personally.
Do you have anything specific? You said it was immediately useful, how so? What from this book (other than classes and subclasses which I am not interested in) did you use in your regular campaign?