A lot of people who are saying the Simpsons are overrated are usually too young to remember when the Simpsons was THE show and was funny as hell. Season 1 is pretty decent, seasons 2-7 are brilliant, season 8 is pretty good and then 9 was just OK and then after that it started to suck. Now I find maybe in a 20-episode season about 2-3 episodes to be funny.
Yeah, I don't think people get just how good that show was for almost a decade, especially for when it was on. It was breaking a lot of ground and considered very controversial. If anything is overrated, it's the formulaic sitcoms with laugh tracks. Unnatural setup, lame punchline, laugh track, commercial, repeat.