Seeing as how I never really properly contributed to the conversation yet, I think I'll voice some of my thoughts.

I'll admit, I kinda fell for the whole hype train thing after I discovered it.  That being said, I feel like my discovery of it was very abrupt and unexpected, and I found myself wondering why the hell I hadn't heard the word "Undertale" before, or anything about the game.  I then felt cheated, because my first exposure to it was a playthrough.  I watched it all the way through, then regretted that I wouldn't be able to play it without getting a more genuine experience.  But even still, I found the concept of an adventure RPG where literally no one has to die interesting, and the way the characters were done, and how the story changed according to your behavior did make it feel more alive than damn near any game I've seen.

Speaking of the whole "your actions have consequences" thing, yes, Undertale does it, hands down, more effectively than any other game I can think of.  The multiple endings thing is nothing new, but the fact that your entire fucking gameplay experience can change depending on how you play it is simply something else.  To be fair, it was a little simplistic, in that you only REALLY see the effects on a genocide run, but the fact that there is such a massive contrast is pretty cool.

Of course, now that I've played it a couple of times and seen multiple playthroughs, I can safely say it's not the greatest game in the world.  It's a pretty damn good one, and I will say I think it's one everyone should play at least once, but it's not perfect.  I think my biggest gripe would be, as has been said before, the tutorial section, and by the same token Toriel herself.  All I'll say about the ruins part is that it was too long, and would have been better were it shorter.

Now Toriel... I honestly just can't take her seriously as a character.  Literally up until you get to the point where you get to her house the majority of her dialogue sounds robotic.  I can't think of a better comparison than the holo-lady VI that tries to guide you around the citadel in Mass Effect.  She sounds like her, and then she does the exact same thing during the pacifist ending when she stops the fight between you and Asgore.  Her character shines at exactly one point, and that is before, during, and after fighting her (counting that all as one thing).  She is essentially a plot device.

But anyways, back to the game itself.  I feel like it's both a good and bad thing that it's been hyped as much as it has.  I feel like it's good, because it's drawn more attention to itself and gotten people who otherwise wouldn't have given a shit to play it, and for that reason, I see it as bringing a refreshing game experience to casual gamers who are used to the simple "Go here, fuck shit up" formula; people to whom Undertale is probably completely different and perhaps even revolutionary (filthy casuals).  And then, on the other end of the hype, there's those gamers who are used to kinda-thought-provoking indie games who get a case of the hype effect and inevitably complain about it a month or so later.

Nonetheless, I do still think it's a pretty damn good game, and definitely one that, like it or not, is probably going to go down in history in some way.