As I just mentioned in an eariler post, Earthbound is an overrated game (and the Mother series for that matter) not necessarily because of gameplay, but because of the rarity of the game. We know that overexposure often leads into the perception of something being overrated, but in this case, it's the relative rarity of this game means that few folks have actually played the game, and they hype it up to a rather obscene limit, also because of said rarity, allows it to go under the radar for so long, and practically charge an arm and a leg for it online. Psychonauts had a similar problem to Earthbound in many ways, it's no stretch of the imagination to say that Psychonauts is this generation's Earthbound, for better or worse.
Speaking of overexposure, Assassin's Creed is another overrated series, not neceassrily because of the yearly releases, but more so being inconsistent in quality and with the MC. The first AC was pretty much average at best, and the dialogue was rather poor, but it started to get much better with Ezio and AC2 and Brotherhood, before sliding down with Revelations and AC3, with Connor Kenway largely being disingenuous and unlikeable. Black Flag might actually be the best AC game, mostly because Edward Kenway is very relatable, the combat is solid and it's so much more fun being a pirate sailing in the open seas.
TL;DR version: Earthbound overrated because of rarity and fans jacking up the price, AC series overrated because of inconsistencies in gameplay and MC.