This game is definately one of my favorite games of all time. I've played it again and again, and I just keep coming back for more!
Anyways, here's the basics behind the game: it's an RPG set in the 1990's. This automatically sets it apart from pretty much every other RPG out there, and makes for an interesting game. You'll ride the bus, use pay phones, and get cash from ATMs. It's a nice change of pace from your usual medieval setting.
Graphics:
The graphics are simple, but really... by todays standards, pretty much everything on the SNES looks dated. I have no problem with the graphics, but that could just be the fanboy in me talking. Don't expect Chrono Trigger (or even Final Fantasy VI) quality.
Sound:
Personally, I love the sound in this game. A few of the songs are memorable, and overall the sounds and music fit the atmosphere of this game. You'll hear some belches and burps from certain bad guys, which is always fun.
Gameplay:
Earthbound is a fairly simple RPG. There's no in-depth stat development, and the battle system isn't complex. This game shines when it comes to the overall gameplay experience. The characters are wacky, the storyline is fun, and overall this game can be described in one word: different.
It's hard to pinpoint why this game is so fun to play, but the fact that it's different is probably a major factor.
I won't bother reviewing control, since it's an RPG... the controls do everything you need them to do, and I personally have never had a problem.
To wrap things up: if you're an rpg, give Earthbound a chance. It's an experience everyone should have!