I feel compelled to explain this old rating seeing as so many people love this text. So here goes:
Basically I felt it had great ideas about the horror and tragedy of war. But I've read so many books about the wars. This didn't have the same impact as say The Book Thief or All Quiet on the Western Front for me. It didn't present anything new for me. Except some philosophical thoughts that didn't really mix with my own thought system and so it felt weird. Perhaps it gives a good indication of what it's like for someone without my views to read say The Chronicles of Narnia...except that personally the story of Narnia makes far greater sense.
That's basically it in the end. Slaughterhouse Five didn't make sense. It was too random, too abstract, leaping here and there without properly explaining to me what the heck was going on. Simply put it's not my style of reading. Sure I'm all for abstract rather than linear narrative progression (I'm a very abstract person myself) but it's still up to the author to engage his readership and to provide a clear guiding path through that narrative. Perhaps to put this simply Vonnegut's quirkiness clashed with my own quirky, whimsical, enigmatic, eccentric personality...
Although with all the adverbs that's hardly simple now is it?