In 2001, "K-PAX" hit theaters, starring Kevin Spacey as the enigmatic Prot, a man who insists he's arrived from the distant planet K-PAX, orbiting a binary star in the constellation Lyra.
He's brought to a Manhattan psychiatric institute, where he meets Dr. Powell, who tries to unravel the mystery of this puzzling being. Prot's time on Earth is limited — he already knows exactly when he'll return to his home planet.
Interestingly, Spacey was originally supposed to play the doctor. According to "Wikipedia", the role of Prot was offered to Will Smith. But the actor insisted on his choice, and we ended up with one of his most mysterious and nuanced transformations.
His counterweight came in the form of Jeff Bridges — as the psychiatrist who seems to be treating others but is actually searching for answers himself.
The film was directed by British filmmaker Iain Softley, based on Gene Brewer's novel written six years before the movie's release. But critics note that the film turned out even deeper than the original.

Source:
imdb.com
What do critics say?
"Works even better than the novel," writes Kathi Maio from The Magazine of Fantasy & Science Fiction.But Cinema Crazed accuses the film of being slow. EmanuelLevy.com goes so far as calling it a "ridiculous therapeutic melodrama." Still, even negative reviews admit: the scenes between Spacey and Bridges work on such strong contrast that they hold interest even among skeptics.

Source:
imdb.com
One Rotten Tomatoes user named Arlene M even confessed:
This is one of my favorite movies, and most of my friends agree. The actors are great. The story is great. I'm going to watch it for the third time soon.
If you're looking for a film that simultaneously soothes and disturbs, makes you doubt, and somehow offers hope in the end — watch K-PAX. Maybe you'll want to believe there's a planet out there where everyone understands everything. And nobody lies. Earlier on zoomboola.com, we told you about "Reign Over Me" — when Adam Sandler makes you cry instead of laugh.