I still remember when it first aired, I was quite surprised it was a double length short. Yes, Rocko had done double length previously ("I Have No Son", and later the excellent "Wacky Delly"), but it was a rarity for this show.
I agree it's one of the more "serious" episodes. Still quite funny at parts, but definitely bittersweet, with Rocko experiencing empathy for old people and the old people, now young, getting to have a second chance to be youthful.
Izzy Mandelbaum: How 'bout that, huh? The WORLD'S greatest dad. My son made it for me.
Jerry: That's very nice.
Izzy Mandelbaum: The best in the world! Which means I'm better than just number one.
Jerry: Well, I don't know how official any of these rankings really are.