I came to Slaughterhouse 5 having categorised it in my head as an SF book, which I think rather miss-sells it. The notion of Billy Pilgrim being "unstuck in time" (a wonderful phrase, now much stolen), lets the author move about in a non-linear style through the plot, but it's not the engine of it. This is a World War 2 novel first and foremost, and a very good one at that. 
 There's possibly not a lot more to say, as I really can't fault it (neat construction; ironic prose; funny, vivid characters), but Slaughterhouse never *quite* grabbed me emotionally in the way that my favourite novels have. It feels like an attempt by the author to process the huge loss of life he witnessed in Dresden at the end of WW2, and so everything is pervaded by a dazed, numbness, which I assume is rather the point.