Now doesn't that make you feel better? The tumblrinas won tonight, now they can play their meme game soundly, and everything is all right.
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Aight, real talk. There is definitely some salt going on from both sides. What I am seeing is of course disagreeing with the decision because, well, the game is popular, and I understand, however maybe that isn't the best reason to disagree or not like something since it is popular to not like something because it is popular. Personally, I disagree with this for a different reason.
While I do think Undertale is a good game, GOTY it is not. Now, this may be too much to swallow for Undertale fans, but what we have is the indie game of the month, that relies to heavily on the atmosphere and tone of Earthbound\MOTHER, "retro graphics," use of lame anime and spaghetti jokes when there aren't actual amusing things going on, and the "MUH MONSTERS ARE PEOPLE TOO!" shtick. Also, doing a pacifist run in a game is not new. You can do that in many games like Deus Ex (although you have to kill certain characters in the game, however you can do so indirectly through certain dialogue options) and Thief 2, and even some traditional RPGs as well, most of them being of the Western and Computer variety. If you think about it, for all of those reasons it just is not enough to be one of the best games of all time or even just GOTY.
But I can say this, maybe more people should give the game a try, Toby Fox and his team should work on a game that totally shatters Undertale, especially in its graphics, atmosphere and mood (make it original rather than relying on something many other indie devs are going to use as the standard!) and its portrayal of morality, and more salt must flow.
Personally, as of right now, I am feeling The Witcher 3 is my GOTY, and Undertale gets a strong 6 to middling 7 out of 10.