If the characters aren't real, it doesn't work
Derb responded to a reader's comment ("I tried one of Clarke's novels once, but couldn't get into it. His characters just didn't seem like real people") on Arthur C. Clarke:
Reading sci-fi for human interest is like reading your newspaper's sports pages for stock quotes. That's not what it's about. What's it about? To quote the title of an Isaac Asimov essay on this very topic, it's about "Those Crazy Ideas."
But if you aren't applying "those Crazy ideas" to humans, if you aren't examining or considering the impact on humans, or human analogues, then how do you get emotionally invested enough to maintain interest?
I have never read any Clarke, and don't have any opinion of his writing ability. I can't comment on either his characters or his ideas. But I do know that, with rare exceptions, characters* that don't feel or seem "like real people" really distract from a work of any type. The term "suspension of disbelief" was apparently coined by Coleridge nearly 200 years ago, but it is accurate and widely accepted - the success of a work of art depends on the audiences ability suspend their disbelief of the settings or subjects, to accept the premises on which the work is based. I have no problem suspending disbelief for technical issues (most of the time), for "those crazy ideas," but if the characters don't feel real then it doesn't matter. (Think about how much suspension of disbelief is required to enjoy the Harry Potter series - but it doesn't matter a whit, because Rowling's characters are so vivid and real.)
In short, the "crazy ideas" may be what the author is in love with, what he's most concerned with, but if he doesn't give the reader a reason to care about someone in the book, it's not going to work for most readers.
* - The characters don't have to be real, but they need to seem real. And they don't need to be human. Watership Down is a tremendous work, with characters displaying real human characteristics despite the fact that they're rabbits. Animal Farm works because, accepting the premise, the characters behavior and dialogue are all true to the logic of the situation.