A Genocide run?!

Dude, I... When I think that I must kill Toriel, Sans, and... See the entire world becoming empty... I just can't do it.

Yeah, it does feel similar to Earthbound, though I wouldn't say it's a reason I like it. It came up a couple times when I played, such as "Hey, the interior of houses look similar to Mother 3" and the dialogue is very witty too.  The thing about Undertale is that everything is done with excellence and you can tell a lot of love and care went into this. The soundtrack is excellent, with music that is very catchy and gets you addicted. The characters are great and interesting, becoming characters you like almost instantly. Even enemies have personailty to them. The battle system is great, having a big variety in its mechanics and pretty turning the whole genre on its head. When you feel something may be becoming stale, it introduces new ones to you, and eventually mixes them all together, really testing your skill. There are some mechanics that are unique to enemies, making for some really exciting moments. One particular moment feels like you are doing more than just a fight. There are very wonderful moments that makes you laugh, feel in danger, and even very sad. It even makes fun of certain iconic moments in games. Also, it just plays with your mind and kind of digs into your thoughts...

This game is just beautifully crafted from beginning to end, and almost no moment in it is wasted. I cannot recommend it enough.