This thread has inspired me to revisit other emotionally-charged Season 2 episodes, Bart VS. Thanksgiving is another gem. So many jokes going on and yet very real, heartfelt emotion. They don't make 'em like they used to.
This is why early Simpsons eclipses the modern efforts. The characters were real, not just caricatures. There were no punchlines, there were stories, and no unnecessary wackiness.
That episode is great a long with the other episode about the simpson gene. The one where lisa realizes she's doomed to become dumb until homer gathers all his relatives and tries to show her smart simpsons