I've been having a lot of problems like this with sf in recent years. 100 or 150 pp. into the book, the writer's imagination is dazzling but somehow it all runs together, whatever is or was at stake got lost in the phantasmagoria. It seemed like the only reason for the story's momentum was that the author had a contract to write a 600-page book. This has happened to me with China Mieville, CJ Cherryh, Neil Gaimon, Connie Willis, a.o. writers, plus I preferred a William Gibson short stories book to the novel I read. Although Little Brother by Cory Doctorow is now a favorite.
For a few years late in the sf Golden Era I loved to read Astounding every month, until a barrage of Robert Silverberg cured me. Nearly all of my favorites date from the 1940s and '50s. Delaney, Zelazny, and the other stuff that true sf fans considered high literature bored me. Interestingly, in the late 1960s when I tried to order a book by my hero JG Ballard from an sf specialist store, the owner, a big SF FAN, angrily refused to sell such stuff.
Since the 2 novels I wrote are at heart science fiction, please don't tell my opinions to any of today's true sf fans.