The whole time traveling and space alien theme was a bit odd right till the end, when I actually think I got it. Space sci-fi still doesn't appeal to me very much, though.

Otherwise, the book was good. It was, at least, a different war novel from all the others I've read and heard of before. It was easy to read, as well, especially after I found this Slaughterhouse 5 glossary online:

https://www.cliffsnotes.com/literature/s/slaughterhousefive/study-help/full-glossary-for-slaughterhousefive