Kutcher plays Simon, an investment banker who has quit his job under mysterious circumstances, right before he is to meet his possible future father-in-law (Mac). His girlfriend, Theresa (Zoe Saldana), has refrained from telling her parents that he's a white guy. This sets the stage for the inevitable "What the hey?" moment where Theresa's dad, Percy, (Mac) mistakes the cab driver for his daughter's beau, and Simon is, more or less, humiliated. Ha, ha, ha, ha ... whatever.
Simon wants to be liked, doing his best to bond with Percy and enduring various humiliations such as being relegated to a basement fold-away couch, with the protective Percy as a bed partner (ha-ha-snort-ha ... whatever). During the film's sole eye-opening moment, Percy taunts Simon into telling racist jokes at the dinner table. Everybody laughs until Simon goes too far, and this amounts to one of only a few times the film feels honest and daring.
The movie then veers off the subject of race relations as Simon's reliability comes into question when his job status is discovered, and Percy gets into trouble for not taking his 25th anniversary party seriously. Guess Who becomes just another male-bonding film as Simon and Percy work together to win their women back and provide the happy ending.
While the title and supposed subject matter suggest the film is a remake of Dinner, this one is closer in tone to Ben Stiller's Meet the Parents: A well-meaning young man gets harassed by a psycho father who looks into the man's background info without his permission. That father also does everything he can do to prevent the man from sleeping with his daughter under his roof. The only thing missing is the cat crapping in the toilet.
Kutcher is a decent-enough comic actor, squirming with convincing discomfort and managing to create someone sympathetic in Simon. While he often takes flack for his relationships and role choices, the guy possesses decent comic timing (his dopey character on That 70's Show is pretty funny stuff). Mac is a credible enough grump, although his character here is totally unlikable. The script tries to give Percy some sort of redemption, but he never rises above the level of certifiable nut.
At the risk of sounding a bit cliché, I will go ahead and advise those curious about this one to wait for the video. It's a harmless, safe comedy about a subject that perhaps requires some more edge and brutal honesty. Guess Who would like you to think it's about something substantial and important, but in the end winds up being just another crazy daddy movie.