When Mark Duplass hoisted a stereo over his head to win back his character’s love interest in the opening minutes of 2005 road-trip dramedy The Puffy Chair, a mild generational shift took place. I’ll restrain the hyperbole of declaring a new generation being born, but in paying homage to John Cusack’s grungy romantic tactic in Say Anything, the scene not only re-contextualized the act within the lackadaisical hipster mentality of the new millennium, it juxtaposed contemporary 20-something culture with its aging late-1980s forebear.

And where was Cusack around this time? That same year, he starred in Must Love Dogs -- a feeble attempt to retain his faded rom-com charm -- and Harold Ramis’s The Ice Harvest, a finely tuned comic noir that proved to be the ideal match for Cusack’s maturing visage. He’s still top-notch when playing the soft-spoken loner, but his hopeless romantic roles stopped working 10 years ago.

There’s a danger to Cusack growing up, and it lingers in nearly every frame of his latest vehicle, Martian Child. As science fiction author David Gordon, whose life as a recent widower leads him to adopt a young boy, Cusack has entered the derivative Burgeoning Father zone. I haven’t read the source material (a short story by David Gerrold), but the decision to turn it into a PG-rated family drama seems bound to its premise: The writer gets a taste of his own genre-soaked medicine when it turns out his adopted kid, 6-year-old Dennis (Bobby Coleman), thinks he’s from Mars.

Of course, Dennis isn’t really from Mars, and this particular personality quirk is one part of several problematic tendencies, including an aversion to sunlight, antisocial behavior and major pre-adolescent kleptomania. Discovering these problems one by one, Cusack’s scribe shrugs and sighs, moans and mutters, tries to befriend his kid before losing his temper. It has to be the actor’s dullest, most uninspired performance ever. He shows no serious drive or subtle motives, nor any quietly conveyed wit. I’m all for actors playing against type -- as Cusack does with remarkably effective restraint as an Iraq war widower in next month's Grace is Gone -- but I’m not so keen about watching them play against their strengths.

In both concept and execution, Martian Child comes across as a children’s book remix of the memorably enigmatic K-PAX, a 2001 drama starring Kevin Spacey as a mental patient who claims to have extraterrestrial origins and Jeff Bridges as the shrink who almost believes him. Replace Spacey with Coleman and Bridges with Cusack, drain away the pervasive sense of irreparable despair, and you’ve got one bland family film. Like Spacey’s character, the adoptee in Martian Child has a dark history (some kind of parental abuse) he attempts to assuage under the umbrella of fantasy. But the difference is that K-PAX’s attention to character development almost gets us to accept Spacey’s delusion, while it’s clear from the outset that this so-called “Martian” child hails from Earth.

With "quiet" and "withdrawn" as his main character traits, the kid leaves it to Cusack to breathe life into their shared scenes, but as David he reacts with such tedious frustration that the supposed emotional undercurrents of the situation never blossom. The potential for irony gives way to cheesiness: When the kid tells Cusack about his Martian powers, the writer replies, “I deserve you.” It comes across with the sappiness of “You complete me,” rather than some insightfully funny aside.

The director of Martian Child, Menno Meyjes, last directed Cusack in the atmospheric period piece Max, about Hitler’s art teacher. The effectively foreboding aura of that film is hardly discernible here. There are dark elements lurking in the corners of the plot, but their outcomes are glossed over with gooey conventions. The movie has two climaxes, both using the same Electric Light Orchestra song. That’s one of several uninspired motifs repeated in Martian Child, which seems to rely on redundancy in order to skirt its lack of original ideas, including Cusack’s character. He’s just a cardboard archetype. Gone are the days when this talented actor could say anything and charm audiences. In derivative stuff like this, Cusack would be better off saying nothing.