The dictionary definition of "Killer-App" would probably read Super Mario World were it not just a geek's term for a bloody good game.

This game was to SNES what Super Mario Brothers was to NES, the game that  launched a thousand systems, the one that set the standard for the console from the start, the game that made people go "f**k me!" and "golly, that's a handsome looking game" and the game that made young boys want, nay, NEED  the console.  

It is hard to describe something so good and feel you are doing it justice.  You know the parts that make it technically good, the gorgeous graphics and  vibrant colours, the catchy and perfectly suited soundtrack and sound  effects, the huge amount of levels and amount of challenge in finding  everything. You know about the perfect gameplay mechanics, the precision  control that never lets you blame anyone but yourself for failure and the classic platforming action of Super Mario Brothers mixed with a healthy dose of puzzles. 

What you cant quite put your finger on though is that special something that ties it all into such a lovely package. The bit you feel you should say in a  review but you cant put in words. I don't know what it is, but maybe it's  the searching that will bring you back to play this again and again. This is quite possibly the best video game ever; the nearest I have seen a game get to perfection. I can't make you buy it but what sort of fool wouldn't buy  near perfection for $3?