Earthbound. It's got pretty much everything an RPG needs: story, graphics, deep gameplay, variety, and something that is seemingly lost in RPGs today; comedic relief. I honestly love Chrono Trigger, Dragon Warrior, and a little bit of Final Fantasy. But the only reason I rarely play them as much as Earthbound is because it's SO boring to constantly listen to all this backstory and explanation. That's good that they have that, because it's taking a step forward in storytelling in games. However, it gets monotonous to hear the same formula: "Long ago, in (the dark ages/long time ago) in the land of (random name), there was a (mystical relic/war/hot princess). However, (bad guy does something with that war/relic for his own benefit and/or the nation's deterioration). The land of (random name) began to perish, but then the golden hero with (a defining trait) named (random name from a religious text) came in and kicked the bad guy's butt and then everyone was happy again. Now the bad guy's doing it again, and you have to stop it because you descended from that hero. Go forth and grab the (random # of mystical relics) to restore peace and destroy that evil guy."
Earthbound just has aliens invade earth and then some careless mother let's her child trust a time-traveling bee to go out and defeat that alien. However, his fat-next door neighbor decides to join the alien, so now it becomes more funny to see that fat kid taunt the protagonists so childishly. It's also funny to see all these pop culture references like the yellow submarine, Mr. T, and a lot of similarities between soundtracks and other famous songs like Johnny B. Goode. They also have mystical relics that have little to no relevance to the story. Once during the end boss sequence, you'll hear about this "Apple of Enlightenment". That's the only time you hear about it. The game just uses it as a way to tell a prophecy instead of some guy in robes falling from the sky and warning the bad guys of their defeat.
In short: I like Earthbound because it is different, it uses creativity, and it makes pop culture jokes. I think those earn it the title "greatest game of all time".