it is a quite slow pace face-to-face Brynner/Douglas...i found there was some pretty heavy violence/gore but you know, seventies giallo style : (maybe some spoiler ahead) a little bit phony and fake but the image is there : the monkey torn apart, the flesh torn from the mechanic, etc...
i don't remember if it is alike the novel...but overall i think it is a OK action flick, hero flick : he stands all alone at the end, all the bad guys are out..........
and nice images too : a small rocky island, the sun over the sea
but not a typical Verne's story-on-cinema : subs, sci-fi; but the adventure seen in a lot of Verne's novels tough