Community Picnic probably isn't the best installment of the series, but it has a fair amount of laughs and is noteworthy if for no other reason than it's basically the end of the first era of the show. This is the last episode including Sylvia Field as Martha Wilson, and she did not get the sendoff such an important and friendly character deserved. By the time of the next episode, she had left on a trip, presumably to see George, and was spoken of only once after that.
You get the feeling in this episode that the characters know Martha is about to head out and that her and George's days living next door are numbered, but we don't.
Indeed, it's the last episode with any feel reminiscent of the first three seasons, and in retrospect would have made a good series finale. In those days, shows didn't get the kind of finales we have today. They were all just another episode, but this would have been a good one to end on.