I've played through Undertale's pacifist, got the true ending, and even did a neutral run. I'm working on Genocide right now, but i'm stuck on Undyne the Undying.
Anyways, I don't think Undertale is nearly as emotional as everyone makes it out to be. Don't get me wrong, it's a fantastic game, but I never really connected or cared about any of the characters. Honestly, I killed Toriel like 3 times before I finally figured out the Genocide run correctly, and it didn't bother me. I just couldn't give a **** about the characters, because they weren't there long enough for me to do so.
Also, Toby Fox should be ******* glad the Sonic tweets mentioned his game, they're hilarious.