Was hardly his biggest fan. Can't help but think of how Larry Niven and Jerry Pournelle in their novel Inferno (A tongue-in-cheek retelling of the first volume of Dante's The Divine Comedy), relegated him to the Circle of Heretics, trapped in a garishly enormous tomb with a gigantic neon sign blinking over and over again (guess what the sign said). I wouldn't wish such a fate on the man--I don't think anyone deserves to be the victim of that kind of bad taste--but I can't help but think that Niven's rant ("he knew better!") had a point. Vonnegut's writing did at times get lazy, and he did at times seem complacent in his legendary status.
Of his works, a sentimental favorite would be God Bless You, Mr. Rosewater--mainly because when I read it years ago I wished I had the guts to live life the same way (I'd hate to read it now; it mightn't survive the experience). Mother Night was fascinating for the way, as David Pringle pointed out, it sustained the ambiguity (hero or heel?). I liked maybe one or two of the stories in Welcome to the Monkey House--well, okay, I liked one mainly because of the TV movie made out of it, and not so much because of Vonnegut's story as for the opportunity to see Jonathan Demme work with Susan Sarandon and Christopher Walken (as a nebbish, yet!) together on a romantic comedy. Walken, incidentally, seems to me to be the most convincing Stanley Kowalski I've ever seen (and yes, I've seen Kazan's version).
Cat's Cradle is my unsurprising favorite, maybe the rare--or even one--time when Vonnegut's humor and despair were in perfect balance, sketching a portrait of a mad scientist and his dysfunctionally unhappy family, the birth of a cheerfully nihilistic religion, and the end of the world through crystallization (did this provide the germ for Ballard's hauntingly beautiful The Crystal World--my favorite end-of-the-world scenario--published three years later?). Vonnegut seemed to have said it all with this one (unfortunately he wrote for several more decades ("See the cat? See the cradle?")). But for this and a for a few others of his early work, I'm grateful for him.