The book is Heaven's Fall
by David S. Goyer and Michael Cassutt, and it's the sequel to Heaven's Shadow and Heaven's War, neither of which I saw. Fall is an Ace hardcover, coming on August 6th, and it looks to be set a generation after the earlier books, so it might well stand on its own. The backstory takes its cue from Greg Bear's Eon (and/or The Forge of God): a gigantic Enigmatic Space Thingy (dubbed Keanu, which might be an indication of the kind of humor to expect here) appeared in the sky twenty years ago, and transported a whole bunch of humans into its large (and already inhabited) interior, as part of a war between good and evil alien races. (It's not entirely clear to me if the races are good and evil, or if it's just that one of them wants the Earth for its own purposes, and the other doesn't.) Anyway, by the time of Fall, the Space Thingy has gotten back in contact with Earth to find that the evil aliens have conquered it -- all but for the few redoubts of plucky rebels, of course. I won't pretend that this is a story none of you have ever seen before, but Goyer and Cassutt are both smart professional writers (mostly for various screens), and I'm sure they provide lots of moments for popcorn-chewing.
