Like my last review, this book is the middle of a trilogy. It follows Cosmonaut Keep and precedes Engine City. Though more self-contained than some trilogy volumes, I'd still recommend starting with Cosmonaut Keep, and judging by the ending, it would probably be better to continue promptly with Engine City.
MacLeod continues to explore an interesting society which combines humans, aliens who are the humans' technological superiors but on a basically human level, and other aliens whose intelligence is so far beyond human that they are to some extent gods. He combines interesting speculation with a wild and crazy romp, and manages to work in some interesting insights into gender roles and also the responsibility that the powerful have to the less fortunate.
If science fiction is the literature of ideas, MacLeod is definitely one of the most exciting writers writing today, and he's in top form in Dark Light. In terms of more down to earth matters of plot, the story has some issues of believability. It's a little hard to swallow that the human society that forms the stage the characters act on would actually respond to the events in the story the way MacLeod has them -- but it's not so unbelievable that it ruins the story. However, I don't think anyone could reasonably accuse him of being either banal or predictable. The characters are interesting. I only actually like a couple of the several viewpoint characters, but it's still interesting to follow the other ones, even when a couple of them are kind of scummy. There is conflict among the main characters, but none of them are obvious villains and at this point in the trilogy it's far from clear who's actually going to come out on top (or even who we want to see come out on top).
All in all, this is a solid book and a fascinating read. I am a little troubled by the unlikeliness of some of the plot twists, and I'm consciously trying to avoid inflating my ratings, so I'm going to give it an 8 out of 10.