TBH I was never into the black and white aesthetic of Undertale. Some of the sprites were just a liiiittttle to off-looking for me. The overworld looked great, though.
Delta Rune, however, looks FANTASTIC. I'm really interested to see where that game goes.
Oh yeah that's right, I still need to play Deltarune. I downloaded it the day it came out, and got lost in the Smash hype the day after, and then was busy with other things, and forgot about it. But from the glimpses I've managed to see (I've been trying to avoid seeing footage or screenshots), it seems like the artwork took a step up, which is appreciated.
The battle sprites are all mostly okay, but the overworld art is hit or miss. There's some pretty bad perspective in a lot of areas, and some character sprites aren't that great. Which is a shame, since the environments of the game are supposed to invoke emotions, too, and could do so much more if the art wasn't so amateur.