It may not be to everyone's taste or appetite but,
For me, it's an all-you-can-eat buffet of brain food.
It's a hard book to describe. I think some of the criticism about it being over-hyped is might be misplaced, that much of the hype is not just for the book, but for the year-long Drift Crisis event that includes around a dozen different products.
It doesn't have a lot of new mechanics. I think that might be a good thing for this book. It makes it easy to use in any past, current, or future adventure.
It does give new life to content from older books like the alternative faster than light drives in the starship operations manual. It sets the foundation for future mechanics like drift lanes. It creates variations for running old APs with a new twist. It's a book that turns drift travel from this is how we travel in Starfinder into the drift being one of the coolest features of Starfinder. It's the book that suggests the drift can be hacked. If you can hack the drift the possibilities are unlimited.
It's not a book for everyone. It's not a reference book you need at the table every game. It's good for players who want a character with a background connected to the drift. It's good for GMs who like the extra flexibility or variation it creates in the story, or are looking for 20 new adventure seeds. I think it's also meant for the developers of Starfinder as a foundation for the future.
I like that Piazo is willing to try something completely different, not every book can be this outside the box, but once in a while, it's a great way to keep the game fresh.