There are just too many mysteries in this film.
Mystery #1: When Prot (Kevin Spacey) arrives suddenly in the middle of Grand Central Station, did he arrive on a beam of light or on the 4:17 local?
Mystery #2: When Prot is then hauled off to a tony psychiatric institute in mid-Manhattan and treated by Dr. Mark Powell (Jeff Bridges) for severe psychological trauma, is it he or the doctor who is crazy?
Mystery #3: When Prot seemingly can describe a remote corner of the universe and wow a bunch of hardened astronomers sitting in the new New York planetarium, is he really proving he's an alien? How about when tests show that he can detect ultraviolet light, far beyond the range of what humans can see?
Mystery #4: When Prot brings sweetness and light to the mental patients in the ward around him, is he proving the superiority of his planet's social systems, or just the compassion of a guy deeply hurt? How about when he brings his stereotypical workaholic doctor closer to his estranged family members?
Mystery #5, the most interesting mystery of all: When the director (Iain Softley), writer (Charles Leavitt, working off the novel by Gene Brewer) and director of photography (John Mathieson) sat down to discuss making K-PAX, had they resolved these questions for themselves or had they just decided to inflict the undramatic uncertainty of Prot's identity on their audience just to see how it came out?
As any fan of mystery novels will tell you, the joy of the read is in the pilgrimage to knowledge. In the hands of a good author or director with a clear vision, a good mystery is an unparalleled pleasure. It doesn't always require a concrete solution, but it does demand a coherent stance so that you might journey with the author. By contrast, K-PAX suffers from a lack of coherent conception, lacking emotional resonance in virtually all the areas where it seeks to make a mark. Refusing to take a position themselves on whether Prot is alien or human, playing coy with the audience and the protagonists, the main characters are continually undermined and cease to be captivating about mid-way through the film.
The texture of the film helps not at all. Most of the "action" takes place in therapy so that the movie spends most of its time in talk talk talk talk talk. No white space on them pages, just a lot of therapy where no one, not the patient, not the shrink, not the audience, really cares what is going on. What sympathy we do gain for Prot is shattered in the last third of the film after we've come to fully believe he's an alien and then Dr. Powell goes on a trip to prove that he's not.
It's a pity that the story is so very dull, because the filming itself, by contrast, is quite pretty. In keeping with this theme that Prot is a light traveler, jeweled glass boxes are everywhere -- from Powell's house lit at night to the paperweight that sits on his desk in the sun. Photography director Mathieson makes much of the fact that film is a medium of light, and if he overplays his hand somewhat and makes too much of a contrast to the pedestrian script, you can still forgive him for at least making things a little bit interesting. The rest of it -- the mysteries that can't be solved, the characters that won't take root, the old story of the patients curing each other -- can just stick around waiting for a better script.