This is probably my favorite thing Toby Fox has made so far. Undertale and Deltarune Ch 1, I felt that he was really good at writing comedy but was less consistent with writing more serious, thought provoking content. I think that changed with this game.
Having a party of characters is so good. He skillfully uses splits in the party to help showcase different dynamics between the characters and to keep things fresh. The plot is definitely carried by its characters for now, but I'm okay with that.
Gameplay has also improved. I think the spare percentage system instead of a binary spare/no spare thing is great.
Update: I played through Snowgrave and it was raw as FUCK compared to the genocide route of UT