BY LARRY CARROLL | The Godfather films. Glengarry Glen Ross. Scent of a Woman. Heat, Scarface, The Insider, And Justice For All, Donnie Brasco...it's mind-boggling to think of all the great performances Al Pacino has given. One would be hard-pressed to find an argument that he is one of the greatest actors to ever grace the screen, and now that Pacino is into his sixties, he could very easily retreat into the life of award ceremonies, celebrity golf tournaments, and cameo appearances as do so many other actors of his status.

But the thing that has always marked the thespian's remarkable career is his gutsy choices in what to do next. After he achieved prominence playing Michael Corleone, Pacino had Hollywood throwing hundreds of scripts at him. But instead, he chose to take on edgier projects that challenged him, like the blacklisted cop in Serpico or the sexually confused bankrobber in Dog Day Afternoon. Through the years Pacino has never been one to take the easy payday; how many actors could play a Cuban drug kingpin (Scarface), a blind Army Colonel (Scent), the mayor of New York (City Hall), and the human incarnation of Satan (The Devil's Advocate)?

You would think the guy has shown us everything he has to offer - every accent, every bugged-out reaction in those eyes, every nuance of his abilities - by now. But if you were thinking that, then you haven't seen Insomnia yet. He has taken on a role that calls for the actor to tear himself down until he is a shell of his former self, something that requires some real talent, and it pays off in one of the best performances in Pacino's career.

Cast as veteran Los Angeles detective Will Dormer, Pacino plays a policeman of such acclaim that he writes textbooks quoted by young cops as though they were sacred scripture. In a majestic opening sequence, we watch Dormer and his partner Hap (Martin Donovan, The Opposite of Sex) fly over a field of peaceful but menacing ice formations and into a small Alaskan town named Nightmute. They have been called in to assist the local authorities with their investigation into the murder of a seventeen year-old girl.

The weathered veteran has handled this kind of thing a million times before, but there's something different about this case. Most notable is the locale; the detectives have arrived during Midnight Sun, a yearly period in the region during which the darkness of night never falls. From the moment that Dormer arrives in the town, he is out of his element, thinking that ten in the evening is actually ten in the morning. Retreating to his hotel room, he tries his best to sleep, but the relentless sun keeps spilling out over the corners of the shades in his hotel room.

The sunshine is contrasted, soon enough, by the thick fog that is present during a sting operation that the detectives organize at a small cabin by the water. When the subject escapes, Dormer draws his weapon and shoots into the fog, fatally wounding Hap. Panicked, Dormer tells everyone that the suspect shot Hap and then fled into the fog.

As revealed by their final conversations, Hap and Dormer are in Alaska for more reasons than are readily apparent to those around them; the Internal Affairs department of the LAPD has been cleaning house lately, and the two men were sent away to get them out of the heat for awhile. Hap was considering giving into the pressure and telling IA about some evidence tampering that his partner might have engineered. When Hap dies in Dormer's arms, the motivations of the detective become as murky as the haze that surrounds the officers.

In the middle of the night, as he lies awake in bed and contemplates what he has done, the detective receives a phone call from a mysterious man. The man insists upon drawing parallels between the two of them, saying that he killed the seventeen year-old girl, and he also witnessed Dormer kill Hap. Now, the detective is trying to solve a murder, while at the same time trying to keep the murderer from getting him thrown into prison first. And as night after sleepless night goes by, his instincts fade when he needs them most.

Pacino's performance in the film is amazing - he comes swaggering into the Alaskan town on top of his game, using his sharp wit and years of expertise to show everyone around him that he is now the big fish in this pond. We watch him fall apart, first as his attention span is diminished, then as his instincts overcompensate and he becomes aware of every movement around him, when he starts messing up his work in ways he never would before, until he's finally in full-on hallucination mode. Pacino plays Dormer (whose last name has an ironic, somnambulistic sound to it) as a man stuck in limbo, forced to confront the sins of his past and decide whether he will allow himself to be cleansed of them.

Robin Williams plays Finch, the mysterious man on the other end of the phone. Standing toe-to-toe with Pacino, Williams reminds us of the humanity that he has brought to his finest roles in films like The Fisher King or Good Will Hunting. This is a film that explores the ease with which someone can take another person's life, and the fact that a killer is not always a hulking, unthinking monster. As Finch engages Dormer in a chess match, playing tricks with his mind that blur the lines of guilt and innocence, premeditated and accidental acts, the two actors force the audience to confront their own notions regarding matters which we all pretend to think are black and white. As much praise as Pacino is due for his expertise in playing a good cop with a dirty conscience, it is Williams' ability to do just the opposite - creating a killer in whom you see shades of your friends, your neighbor, yourself - that keeps your eyes glued to the screen. As the crux of Finch's plan repeatedly reminds us, there isn't that much difference between the killer and the man who's trying to prove his guilt.

Although primarily known as a comedian, Robin Williams has always had a strange, sick edge to him. That bent in nose, that uneasy smile - there's something dark about the man that has never really been exploited until now. He has a certain John Wayne Gacy quality about him - the clown whose smile belies the darkness inside. He is a perfect fit for the part of Finch. Pacino and Williams, both Oscar winners, seem to keep upping the ante on each other, just as their characters do in the film. What results is the best performance from either in years.

Less successful is the third Oscar winner, Hilary Swank, as a young cop named Ellie who worships Dormer and is in charge of filing the report on Hap's death. The character is well written and interesting enough, but Swank doesn't bring it anything that any other actress couldn't do just as well. She never quite convinces you that Ellie's as sharp as the script needs her to be. It is doubtful that her character, as presented, could match wits with Finch or Dormer, even if the both of them hadn't slept in a week. It's not that her performance is bad. It's just that, as constantly illuminated by those acting around her, it's glaringly adequate.

Several of the supporting actors do step up to the plate and swing for the fences with success, however. Nicky Katt (Boiler Room), proves once again to be one of the most promising young character actors working today, bringing a fine skeptical edge to his policeman role. Donovan, meanwhile, makes his few moments go a very long way. The moment early in the film, when his character is shot, is a make-or-break scene in which his character must convince us that he sees the danger within Dormer. When we see the detective's own partner recoil in fear as he rushes to help him, the realization sinks in that Dormer has been walking the line for quite some time. Donovan sells the moment with the look in his eyes. Amazing work.

Director Christopher Nolan, who leapt out of obscurity last year with the indie hit Memento, cements his reputation here as a director to watch. As with that film (and his previous effort Following), there is an undeniable visual style and originality to the presentation of the story. Most importantly, however, he shows restraint; he never gets in the way or feels the need to remind us that he's behind the camera like so many other young directors do. His best moments come during a thrilling chase across some logs floating down a river - Nolan effectively makes the audience hold their breath as his drowning antagonist does the same.

In a film that so proudly revels in its originality and willingness to take its characters in any direction, I must say that it was sad to see an ending that didn't seem to carry the same weight. I guess there could have been worse ways to end the film, but that doesn't necessarily make this one seem any better. The film takes place in a bizarre town overflowing with complexity, and such a simple ending just seems, well, out of place.

Although Insomnia gets major points for the acting, script and direction, it does lose a little luster thanks to Hilary Swank's vacuous performance and the less-than-memorable conclusion. However, a few more points are added back on for the final line in the movie. So many films nowadays don't even try to give a movie a good final thought, one last line that ties everything together, but this movie gives Pacino a real beaut. It hangs in your mind as you walk out of Insomnia, one of the best films of the year so far.

GRADE: A-