This episode had some good laughs, but overall I wasn't too impressed. The secondary story involving Bart and Lisa building a gigantic castle out of cardboard boxes from ASS --which stood for "American Shipping Services," and is not, as one truck indicates, affiliated with the human ass-- and fighting an apocalyptic battle with the men in brown was more entertaining than the main story, in my opinion.
"Those boxes are for shipping, not for creating a world of pure imagination!"
Not to say there weren't some good laughs to be found throughout the half-hour. Homer "Flintstone-ing" his car to save on gas was an immediately classic moment. During Grampa and Selma's courtship, the camera panned past a few cars at lover's lane, stopping at their car that was rocking up and down. Cutting inside, we saw that Selma was giving Grampa CPR.
Patty, disguised as Selma through the perfect placement of a bobby pin, and Homer, disguised as Esteban de la Sexface, also offered some laughs, including Patty envisioning Homer as Mrs. Krabappel and Homer exclaiming to the camera after Selma showed up, "Dos Selmas? Ay-yi-yi!"
The best part of the episode, though? Grandpa telling Selma's daughter a grim tale of his time in the war, but "censoring" it for her young ears and using terms like "machine hugs" and "fun throwers."