I've attended do your own thing retreats and retreats with teachers. I prefer an experienced teacher, preferably one who does this professionally or to work on my own project. I've had a few crazy experiences with mysteries at retreats so prefer to know what I'm doing or have the choice not to do the mystery.
I've only been to ones where meals are cooked for you.
I prefer the option to have a bedroom to myself if possible (and if I am 'new' to the group).
An optional opportunity to make theme blocks and win them can be fun. More than one mutual cutting and ironing stations are a good idea. Taping paper lunchbags to the tables for thread snippets and scraps is helpful.
One retreat at a hotel offers chair massages. The fee comes out of the retreat price and people tip. That was fun after sewing for a long time.
I think some more tomorrow.