I liked Ender's Game. But I never read any of the sequels. I want to say I read something else by him recently about Norse gods in hiding in modern times. Book One of an on-going series. It was not as good as Ender's Game, but not bad either.
Vonnegut's Slaughterhouse 5 is probably worth the acclaim it generally gets. Wasn't blown away by the other stuff by him I've read (which may be just Cat's Cradle).