I am a huge fan of Vonnegut's work and I'm very fond of this movie, but I wouldn't say that this is a film of the "Mother Night" that I read. When people say that Vonnegut is unfilmable, two things come to my mind. One is that many of his themes are very near the knuckle or even taboo, despite the accusation sometimes used against him that he chooses relatively "easy" targets for his satire. This means less every day that passes as far as filmability is concerned. Directors these days appear to revel in breaking taboos and I have high hopes for the version of "Bluebeard" now in production. Amazing to think that an innocent piece like Vonnegut's "Sirens of Titan" would probably have been the equivalent of "R" rated if filmed when it was published back in the 50s, for its violence, language and sexual and thematic content, though it's a tragedy that nobody's come up yet with a filmable script for it. And in the present economic climate, I also hope some director out there is looking closely at "Jailbird", "Galapagos" and "Hocus Pocus".
The other thing is his narrative style, heaping irony upon irony upon irony but still making it hilariously funny. It seems impossible to objectify, and that appears to be the biggest obstacle to making great films of his great novels, because the little authorial comments that colour our response as readers are just not possible in movies without resorting to too often clumsy techniques like "talkovers". Vonnegut suggested that there was a character missing from filmed versions of his work, himself as author/narrator. To its credit, "Breakfast of Champions" (the movie) tried to keep the comedy and came a bit of a cropper for its pains. As did another turkey made from a Vonnegut novel, "Slapstick" in an even more spectacular way.
Still, there's nothing wrong with a director giving us his subjective interpretation of Vonnegut, and "Mother Night" is an excellent example of how, as another reviewer put it, a good director can add a visual poetry to a source like this. But so much of the humour is lost that though it's the same plot, it's not really from the same novel I read. If it had been, I'd probably have been rolling in the aisles laughing a few times watching it. For a reader of the novel, I think a chuckle even at the end is forgivable. The end of the film, however, is truly poignant, and I think one of the film's successes is that it can genuinely leave you feeling that you've watched someone walk a razor's edge between good and evil, and the jury is still out.
Standing alone and of itself it's well worth a look. Technically there are some minor but glaring errors, notably in continuity, and it too often looks drab and theatrical, but most of the time it hits an acceptable note and occasionally shows considerable imagination and resourcefulness. The acting in general is of a high order, even if maybe the dialogue is by today's standards a little stilted.
It survives quite well watching back to back with "Slaughterhouse-5", and there is actually quite a bit more "good" filmed Vonnegut out there, mostly versions of his short stories - "Harrison Bergeron", "Who Am I This Time?" and some other things like, of course, the misfiring filmed version of his very funny but disposable play, "Happy Birthday Wanda June". Also there was an interesting piece , if it still exists, done in the 70s called "Between Time And Timbuktu" which Vonnegut apparently didn't like much, although he was involved in its production, because he felt it misinterpreted him in its generality. He said it reminded him of the bizarre surgical experiments performed in the HG Wells tale "The Island of Dr. Moreau", but it did for many people serve as an excellent introduction to his work.
But if the films don't make you want to go to the superior source material, they're not doing their job.
As the man said, more or less, the big show is inside your head.

I really do fail to see the actual surplus value of this movie. It's not bad enough to be hilarious. There's no sleaze or gratuitous nudity (although there was plenty of opportunity). There's no gore. There's no suspense in the first hour of the movie 'cause there's way to much scenes of tourist having a party and natives playing funky tribal music. That last part was actually funny on many occasions: You see these natives hitting congas and 'jembés' and that's indeed what you hear (badly synchronized) on the soundtrack. But they also added this funky bass-line on the soundtrack. So, where was the bass-player? At one point the natives get angry and start killing the tourists. Why all of the sudden? It's supposed to be because the evil white men build this tourist complex, which according to their myth awakened the wrath of the river-alligator-god (I actually missed the explanation for that one). But the natives did help for several months to build the tourist complex, so why the sudden angriness? And how in the hell did they manage to push the helicopter in the water??? It's all silly and pointless. This movie also features the skinniest Afro-American model I've ever seen.
At one point our heroic leading couple visits this cave where a weird, crazy old man lives. The only point to that scene is that they make the "shocking" discovery that the killer-crocodile is actually an alligator. Crocodile or alligator, what's the difference? It's big, it's made out of plastic and it eats people. All the same to me. The alligator is a rather silly creation. It's very stiff & motionless and doesn't even flap its feet when it swims. The eyes don't even move when they're shot in close-up. I guess they didn't know 'animatronics' back then in Italy during 1979. There's also a lot of pointless inter-cut shots of the local wildlife. I suspect it's stock footage.
Like, I said, the first hour was pretty lame and the only reason I didn't switch off the movie was because my cat was asleep on my lap and I didn't want to wake the sweet thing. But the last half hour of the movie did get better. We finally get to see some action when the alligator swims through a horde of panicking people snapping its teeth and munching on them. The most entertaining (and at the same time funny) scene is when Alice and Daniel drive a van over a bridge and it collapses. We're looking at a matchbox-version of the van falling in the river here. Funny. But nicely shot. In fact there are several other nice traveling camera-moves. Surprisingly for this type of flick. I was gonna point out some stupid details concerning the end of the movie, but I don't wanna spoil it completely, in case you do decide to watch this movie. My advice is to stay away from it. If you wanna see a decent alligator movie, then see Lewis Teague's ALLIGATOR. I admit, that one isn't Italian and isn't a JAWS rip-off, but it certainly is more fun. And if you're interested in other movies made by director Sergio Martino, then I strongly recommend the highly entertaining 2019: AFTER THE FALL OF NEW YORK. That one's an over-the-top rip-off of every possible existing post-apocalyptic-future-of-doom-movie. "Italians" and "rip-offs", two words that go together very well.