In your experience, what is Halloween all about?

Phenomenal excuse to dress up in costume and get drunk
There needs to be more costumed holidays

For me, it's an expression of a particular set of my creativity. The decorations, the show element of it, engaging in various fantasy worlds and dressing up.
It's just fun, and freedom to have fun doing whatever you like!

Letting kids (and kids at heart) go wild with their imagination and dress up.
Meeting/seeing neighbors.
Eating candy.
I feel really sad for all the folks on lemmy having a bad/frustrating Halloween. I think it doesn't have to be that way, but it does definitely take neighborhood-level effort. We're really lucky to live in a big Halloween neighborhood in a walkable area. We saw all our favorite neighbors and met some new ones, and enjoyed all the creative decorations and costumes we saw while we were out.
But the best part of the night is always getting to see people light up when you recognize their costume. Every time I see a kid dressed as Batman and go "whoa there's Batman!" or compliment a princess on their beautiful dress, you can just see them stand up straighter or strike a pose and it's awesome to see everyone dressing up and enjoying themselves. I probably saw a dozen Marios tonight from age 2 to age 20 and every single one of them was over the moon when I complimented their costume.

Speaking as a Dane, where Halloween has invaded in the last 20 years, basically to replace Fastelavn, the traditional spring-based festival of trick or treating, just another excuse for selling stuff.

As a Brazilian, not much. Throughout my entire lifetime, I saw some Brazilians there and there wearing Halloween costumes but it's not as popular here as "quermesses" (kirmess, church fairs, happening mostly on Brazilian's interiorian towns), Carnival, Christmas or some "important" soccer game (such as Corinthians vs Palmeiras, or Flamengo vs Fluminense).
To me, particularly, no holiday (nor soccer games) holds any importance or meaning. In the end of the day, it'll be just capitalism mesmerizing people to spend money on temporary things.

A cash sink that I refuse to participate in
- I realize that Halloween is a commercial event, but I think there are other outlets for criticism of capitalism. Things where you can make a difference and at the same time let the children have fun. I don't think you can change much if you dwell on trivialities that bring people together despite all the commerce. That doesn't seem to me to be the right approach.
  
  I don't mind participating for the sake of making a child happy, yes, or to support a local business.

Family, togetherness, and of course religion. It's really a joyous occasion where we all come together
- What do you mean by religion? Halloween is a pagan festival according to Christian standards. Of course, I'd be right there with you when it comes to the fun festivals of pagans, but is that what you mean?
  
  😐