A "mature" videogame rating is usually meant to warn players -- and parents -- of oozing wounds, virtual nudity or other adult fare. But "Passage," a downloadable PC game released in late November, shows that a videogame can be considered mature for its artful design and emotional payoff.

"Passage" was developed by 30-year-old programmer Jason Rohrer for an indie game exhibition, and before long the game was the subject of intense, sometimes moving commentary among bloggers. It's impossible to discuss the game without trampling...