The story takes place within the premise that aliens have taken control of Earth and Jupiter, leaving human civilization only on other worlds in the solar system. The aliens control Earth to protect other intelligent species (dolphins and such) from humans. These aliens did not come to kill or enslave humans, to take our natural resources, or similar usual suspects in alien invasion stories.
However, that premise plays only an indirect role in most of the story. The story is something more like interplanetary intrigue. There's a secret human organization wanting to restore human control of Earth. The group is lead by Tweed, a former head of the human government. Tweed is assembling certain specialists which he thinks may help his plans. The protagonist is Lilo, a genetic researcher who was sentenced to death for illegal genetic work. Tweed substitutes a clone of Lilo for execution and takes Lilo to a secret facility.
Lilo isn't really happy about being a prisoner / forced employee for life in Tweed's operation. She tries escaping a few times. Each time she dies in the process and comes back as a clone with downloaded memories. Meanwhile, yet another Lilo clone has been activated by an ally of hers in the rings of Saturn. We end up with multiple plot threads with clones of Lilo. Each has the common motive of avoiding the human authorities which will destroy any clone of a person convicted of a capital crime - and of avoiding becoming an involuntary member of Tweed's group.
These plot lines kept my interest while I read the book, but it was disappointing the book doesn't tell us more about the broader picture. Later in the book we are told more about the aliens, their intentions, and the relative place of humans, dolphins and other kinds of aliens in the universe. The manner and context in which we learn these things begs questions and whets one's appetite to see how it plays out. The Ophiuchi Hotline will not satisfy that appetite for more.
As a result, it's the interplanetary intrigue and Lilo's efforts to escape Tweed that make up the substantial part of the book. As I said, I found that material entertaining. On the other hand, it's not the kind of theme that makes a book particularly memorable for me. There is some food for thought, especially in the alien-related parts of the book, but those are somewhat peripheral to the bulk of the book. As a result, I'd mostly suggest it as a book for those more into intrigue SF or as an adventure SF book.