In my opinion, I really like the little stings from the actual game's soundtrack within this, it really makes it feel like an Undertale song.
Otherwise, pretty good, I feel like Undertale is one of those games that we're not ever going to get perfect songs for since it already did such a great job itself; but yeah, worth a listen.
EDIT: Added spoilers because, yeah, that's totally spoilers whoops. Also this is really cool too (spoilered once again):
(Please note that apparently videos don't format any more once they're spoilered, so you'll have to click on the links now. I know, it's terrible, I'm sorry.)