Maybe you already knew that, although you did say that he didn’t have feel for the book

Vonnegut wrote about the film soon after its release, in his preface to Between Time and Timbuktu: “I love George Roy Hill and Universal Pictures, who made a flawless translation of my novel Slaughterhouse-Five to the silver screen. I drool and cackle every time I watch that film, because it is so harmonious with what I felt when I wrote the book.”[2]

https://en.wikipedia.org/wiki/Slaughterhouse-Five_(film)

If those two Vonnegut movies aren’t good then I guess my pick for the best sci-fi movie of the year would end up having to be this Miri reunion , which I liked more than I remember liking Silent Running.