Donald is, without question, an ass, but given the circumstances, it's not like he's without reason. Also no sane person would blame him for wanting to sue the kids for holding him hostage.
The rest of the parents. From a different perspective, this could be looked at as a horror movie than a comedy.
Funny Moments: Ned asks Grover if he's on drugs he quips he's on heroin and Stacy's, he smugly asks Janet "Happy now?"
Realism-Induced Horror: Your own kids holding you hostage and threatening to starve you until you get along. Also, losing your job because your kids left you in the basement so long that you couldn't work.
Squick: Although Grover can cook fancy meals, he and the other kids feed the parents heart-attack inducing junk food.
They Wasted a Perfectly Good Plot: It might not change the detractors' minds but some critics have pointed out that the movie would have been a little better if it just actually on Grover and his family with Grover's parents trying to work out their problems while being locked in a basement.
The Woobie: Gwenna, Donald's wife. It is subtly hinted that Donald abuses her.
