Huh...
I may have hyped myself up too much.
The majority of the writing of this chapter reminds me more of modern saturday morning cartoon shows (Adventure Time, Gumball, etc.) than of the first chapter and Undertale. It's not bad for what it is... just different, and for me unexpected.
I felt the first chapter killed it in terms of meshing whimsical and sometimes wholesome moments with an underlying sense of foreboding, but here they clearly just wanted to find a chapter theme that allows them to just blast you with one crazy idea after the other. I don't think it's gonna age as well, as the first chapter, especially with jokes about blue checkmarks and such.

Enough underhanded complaining now, let's get to what is awesome:
-The gameplay tweaks, just brilliant quality of life stuff, that makes the pacing of a fight feel buttery smooth
-The music, I mean duh, it's a Toby Fox game. The overworld songs all sadly didn't do much for me, but a lot of the little character themes are killer (the DJ robot tunes give me Toejam & Earl vibes)
-All the gameplay switchups, be it how one must dodge an enemy or some of the "arcade sections"
-The new dynamic Susie has, where she is weirdly nice and willing to show affection. I was a sucker for this with Prince Zuko, and I still am.

I don't say this about basically any game nowadays, but when the rest of the chapters drop, I will not hesitate to buy it at full price. Toby Fox is a real deal renaissance man, who keeps making games even though he has chronic hand pains. You may not like his games, but one cannot forego having respect for this man.

The controls blow, the maps however are superb. I'm not a big remake advocate, but doing this with a big development team to make the world more interactable, have more detailed textures, and make some of the mini-games more complex, would be really dope.
Unlike GTA V this one made every area distinct and full of unique landmarks. I wiped my save and looked if I could find every hidden area in a single evening without hints and I did, because even after 10 years I still remember the layout.

Really makes you want to explore.
Doing stunts in the open-world should have an actual reward though.

Ghosting a level with the Path of Silence is one of my most cherished video game experiences.

It's so sick that you can do a running jump over a guard with that costume without alerting him, and even sicker is that it's not tutorialized in any way.

Some levels force combat and play styles too much which is why I took off half a star.

Demo impression:
Now this! This is a demo that got me hooked!
I had a something of a Pavlovian response with this after playing Persona 5: My mouth almost started watering when I saw twinks with drip walking around Shibuya.
The visuals make me want to open up Photoshop and design urban motifs and the English dub is one of the best I've heard in any media. Period.
I will definitely play the full version someday, this scratches all my current itches.

P.S. I already love with all my heart the weird math guy who dresses in all black.

P.P.S. Is this tangibly connected to the Final Fantasy franchise? I know that some of the same staff worked on it, but the moogle, Chocobo and Cactuar chat stickers got me raising an eyebrow.