This is a solid Goodreads "I liked it" three stars. It was a very quick read, and a story that had sufficient thought and ramifications that put it beyond the normal "alternative worlds" novel. It didn't quite reach "I really liked it" because the characters weren't all that engaging or relatable to me, nor do I think I would re-read the book again. 
 In life, there are always decision points. "Dark Matter" imagines a world where you can revisit those points and jump into that reality of the road not taken. It picks a protagonist who has made difficult choices, with both benefits and costs, and shows how deeply he values the imperfect life he has chosen. 
 The end, which could have gone off the rails a bit, goes a little crazy but in a way that ultimately feels acceptable for the story. (view spoiler)[I do think that pulling his wife and kid into a completely random world was pretty reckless though, and will subject them to just as much stress and pain as he's been through. They don't know if they're going into Zombie world or Utopia. And, like him they did not choose to be in the witness/identity protection program because so many of the multitudes of desperately faithful husbands broke to the point of violence. 
 If you think about it, it's a really sad and dangerous ending for everyone involved, which robbed the story of both closure and a bit of joy. 
 His 2-self was too selfish, and the murder of his alterna-wife at the peak of her artistic career was never adequately settled for me. (hide spoiler)] 
 The tl;dr is: too many ideas that weren't explored fully enough, but readably fascinating and exciting page turner.