Just in case, spoiler warning for the comment below.
I had a lotta of fun playing this game. I loved seeing everybody, especially Papyrus and Mettaton (I was so hyped when I saw that Papyrus' scarf-thing was animated, thank you for that detail), and I think everybody was written well! It makes me worried if I try to get other endings (I have only True Love so far) because it's probably going to sting.
I liked Sans well enough before playing, but this game helped me appreciate him better. He's this casual, supportive, funny dude with a good heart who tries to enjoy life despite the circumstances. I guess I could've gleaned these traits from Undertale itself, but this game in particular helped me understand and solidify his character in my mind. I now appreciate Sans, without a doubt (or perhaps, sans doubt, lol).
In summary, very fun game! Everyone was in-character, I loved their dialogue; the art and music were new and charming interpretations of the source material; the stages of the story were great and I liked the nods to Undertale's own story beats (and the puns... I loved them all), and I'm happy this game is a thing. Thank you and kudos for making it.