I kinda had the same feeling with Slaughterhouse Five as you. I know with music this has happened to me...but some albums, if I listen to them enough, I start to really like them. Maybe you should try reading SH5 a few times and see how it settles in...the first time reading it was soo good...
I think his writing really clicks with a particular type of person at a particular time in their life; if either is not quite right it seems reactions range from disinterest to hostility.
I discovered Sirens of Titan and Player Piano in high school and loved them immediately (unlike so much assigned reading) but I'm not sure I'd feel the same if I was to read them for the first time at this stage in my life. For instance, I still enjoy re-reading Hocus Pocus or Jailbird but not so much Slaughterhouse Five. I can't precisely say why, but so it goes...