I'm currently thinking hard what I should do. The reviews speak for themselves, but I rather trust in this community. Is it worth it? Even when on sale?

Try the demo.
https://www.gog.com/game/hello_neighbor_demo

Ah, that demo has evaded me somehow. Thanks, I'll try it!

I think that demo helps scare people away from the game.

Apparently the real game should be worse

That is ultimately up to you but everything i have seen from the game including gameplay, demo and reviews it does look terrible and i wouldn't even touch it with a ten foot pole myself.

I'm surprised this trash is even allowed on GOG but the curating has been a mixed bag so far.

guess I got my answer. Never thought something could top Simon 3D in ugliness, in terms of smooth gameplay and bugginess but I was proven wrong. Thanks

I haven't played it myself so I can't comment on that. But keep in mind that demo Tiny linked to is really the alpha version, not a demo, so it's going to be really buggy and horrible.

Sadly, from many of the reviews and comments I've come across, the "finished" game is just as buggy and laggy and crashy. Also sleepy, dopey and grumpy. And doc.

I watched an LP, but the AI and gameplay were pretty bad. I would like to play it, but it doesn't seem it will ever be fixed, let alone polished.

No

GOG's "curation" process is baffling

According to many reviews, no.