Because it's original, absolutely amazing soundtrack, good visuals, and just a fun game.
But to be honest though, it's not the first kind like it. Cave Story was a S+ ranked Indie game way before it. Not only that, but the developer of Cave Story made it without any money, did it during his free time(alone), and made it free.
Cave Story to me will always be the golden ticket of Indie games. Games will be close, but most will fall short in some way.
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12/22/2016- Made a bet with Ganoncrotch that the first 6 months of 2017 will be worse than 2016. A poll will be made to determine the winner. Loser has to take a picture of them imitating their profile picture.
