Almost from the start of production, "The Island of Dr. Moreau" was plagued, with reports of temperamental stars (Rob Morrow left), a troubled director (Richard Stanley was replaced) and an overall troubled set. Alas, the truth is in the pudding. This unfortunate adaptation of the 100-year-old H.G. Wells novel contains an acutely unfocused script and intentionally over-the-top performances by Marlon Brando and Val Kilmer. br>   The story--filmed twice before, once in 1933 and again in 1977--concerns a mad scientist (Brando) whose attempts to create the perfect being have resulted in a species of half-human/half-beast utants. Moreau's island lair is discovered by a plane crash survivor (David Thewlis), rescued from the Java Sea by Moreau's assistant (Kilmer). The story is a free-for-all, with no clear plot ine and no unifying theme. Rather than a cautionary tale about a man playing God, it ends up a freak show of misshapen and stunted creatures who spend the final 40 minutes of the film on a rampage. Brando makes his entrance in kabuki-white makeup, a white caftan and matching gauze head scarf. His ludicrous appearance is on a par ith his performance. Adopting a fey, British accent and unapologetically campy mannerisms, Brando is a joke. Sadly, so is al Kilmer, who apparently decided to play a mocking attitude rather than a character. Only David Thewlis takes his acting esponsibilities seriously, turning in a professional job. In its favor, the film has an eye-catching opening credit sequence, lush scenery and some nice camera work. Surprisingly, the fake-looking mutant creatures don't present much of a problem, because they give the picture a welcome, retro-'40s feel.    Starring Marlon Brando, Val Kilmer, David Thewlis and Fairuza Balk. Directed by John Frankenheimer. Written by Richard Stanley and Ron utchinson. Produced by Edward R. Pressman. A New Line release. SF/horror. Rated PG-13 for sci-fi violence, horror and gore involving mutant creatures. Running time: 95 min.