Agreed! These sound tracks are soo good. "Megalovania" is great and Papyrus' theme fits his character perfectly.
Donkey Kong Country Tropical Freeze has some wonderful soundtracks as well that fit nicely with the level's peculiarities (unfortunately the dynamics are not reflected in the videos):
Regarding credit songs, "Still Alive" from Portal is good, too:
EDIT:
The Legend Of Zelda OST are pretty neat too:
finally something in my field. soundtrack 7 the Shepard from FrostPunk played when playing "time to stop time" fits the mood perfectly.
if i ever need a "power trip" feeling where your OP in said game. i just pop this track in and play this game and boom its relaxing.
I'm a nintendo nerd. Koji Kondo's work in the Zelda and Mario games are always at the top of my list. Metroid, Castlevania, and megaman all have fun tracks too. Cant ignore Donkey Kong.
Bastion, and indy game that came out in 2011, has a great soundtrack.
Assassin's Creed Black Flag was fun for me with all the sea shanties.