ONE FLEW OVER THE UNHOLIEST OF CUCKOO'S NESTS.

Byline: Glenn Whipp Film Critic

SATAN CHECKING himself into a mental institution is the intriguing premise at the heart of ``ER'' star Eriq La Salle's directorial debut, ``Crazy as Hell,'' which blends the voyeurism of ``Big Brother,'' the pop psychology of ``What Dreams May Come'' and the screenwriting techniques of M. Night Shyamalan into a fairly engaging, if overly simplistic, comic thriller.

For much of its running time, La Salle's movie seems little more than a pastiche of other films set in mental hospitals. Then comes the revelation that justifies the two-dimensional approach, even if the eye-opener manages to raise as many questions as it answers. Certainly it explains why the line ``a man's environment is the extension of himself'' is repeated several times through the film.

The man who first utters that mantra is psychiatrist Ty Adams (Michael Beach), who has come to the Sedah State Mental Hospital (filmed at a Pasadena estate) to tout his nonmedicinal treatment techniques for a documentary. Adams will live at Sedah and treat a selected group of 10 patients for 30 days, his every move monitored by a film crew headed by a craven filmmaker named Parker (John C. McGinley, playing, if not the devil, certainly one of his top lieutenants).

Adams disdains medication. The hospital's administrator (Ronny Cox) believes Adams is a quick-fix artist who has come to his hospital simply to further his fame. What's not open to debate is that Adams has a God complex rivaled by none.

Enter Satan (La Salle). Listing his gender as both male and female (La Salle makes like Grace Jones in a leather dress), his social security number as 666 and ``tired of being blamed for everything'' his primary reason for seeking help, the devil arrives and, sure enough, upsets the apple cart.

Soon, Adams is sweating profusely (the air conditioning is supposedly on the fritz), having animated conversations with himself and wondering how this new patient can simultaneously have the fingerprints of Dillinger, Dahmer, Milli, Vanilli and six other notorious figures.

Yes, ``Crazy as Hell'' has a sense of humor. (At one point, Satan says, ``I'm great at the box office. At least, I hope I still am.'') And the movie looks good. La Salle, shooting on high-definition video, displays a knack for fluid camera work and arresting visuals.

But the documentary element of the plot goes nowhere and doesn't even really figure into the gotcha ending. Apparently, it was inserted for budgetary reasons - La Salle needed a reason to keep the action primarily in one location.

Another handicap can't be as thoroughly discussed without spoiling things. Let's just say that the devil's in the details and screenwriters Erik Jendresen and Jeremy Leven (adapting Leven's 1982 novel, ``Satan: His Psychotherapy and Cure by the Unfortunate Dr. Kassler, J.S.P.S.'') haven't thoroughly plugged all the holes in their approach. The film's last shot, though, superbly illustrates how the road to hell is indeed paved with good, if deluded, intentions.

CRAZY AS HELL - Two and one half stars

(R: strong sexual content, violent images, language)

Starring: Michael Beach, Eriq La Salle, Ronny Cox and John C. McGinley.

Director: Eriq La Salle.

Running time: 1 hr. 53 min.

Playing: Laemmle's Sunset 5 in West Hollywood; Magic Johnson Theaters in Baldwin Hills.

In a nutshell: A fairly engaging, if overly simplistic, comic thriller.