Excellent review, thank you. You capture the vividness of it very well.
I will add a disclaimer, if you are talking about Goekna / Dhamma.org retreats. They are absolutely not just about technique or dogma-free, despite their marketing. They are overtly religious and the entire retreat is couched in hand-wavy woo.
The retreat itself was amazing. I went to one in Quebec. Excellent facilities, crystal clear skies (it was -25 C out), very soothing place. Food was excellent and overall, the physical aspects were not nearly as trying as I was expecting (though my back was kill after a couple days). I would recommend bringing a sleep aid if you are used to not sleeping so early (they are accommodating). I went a few days without using it, but it is hard to meditate after a sleepless night.
I was very excited. The place had been hyped up as dogma-free. Sam Harris's Waking Up book seemed to encourage it. No mystical teachings. Just a great practice. No communication. No speaking, writing, reading. Not even eye contact to avoid non-verbal communication. I love the idea.
The moment I first sat. . . well, here is the type of sound they pump in: https://www.youtube.com/watch?v=GqEWTlaweaM
The reason for this, in their words, is that the chanting of ancient Pali gives off good vibes. Next, they ask all the students to start repeating phrases in Pali. It feels incredibly cultish at that point. The voice of the instructor during key meditation lessons is intentionally over-accented (you can hear Goenka speak just fine at other times). In other languages (not English) the instructions are clear and concise. Only in the original recordings do you get this woo-y voicing.
Finally, you do get sustained language, in the form of the nightly discourses. After having no other serious language input, every night there is an hourly discourse. By that time you're dying to relax a bit, and if you're like me, desperate for communications so that even a cereal box label would be spellbinding.
The lessons are very anti-science and very religious. Goenka explicitly states the purpose of meditation is to purge your deep-seated sins (sankhara I believe was the word he used) so that you can re-incarnate better. He was clear to point out that the study of physics is unnecessary because Buddha had discovered physical secrets long ago. Literally, he makes a point that Buddha determined the vibration of subatomic particles (even though the numbers provided are wrong, and the premise is nuts). He even goes out of the way to criticize a scientist involved in the work of the cloud chamber, saying that the scientist was always unhappy and thus should not have bothered trying to discover things.
Even the non-anti-science parts are a bit off. At one point, during a lecture on not murdering any living being (acceptable, sure), he goes as far as mentioning that "a cat killing a mouse is not following its true nature". Questioning these things gets you a warm smile with a condescending dismissal.
Here's an example of the course: https://www.youtube.com/watch?v=oJxuIMGC9s4
I only mention all this because HN readers are probably less woo/religion minded than most, and Dhamma.org portrays it as no-woo when it is full of it. The annoyance caused me to drop out of the course on day 6 as I could not stand the indoctrination side of things. Physically I was fine and enjoying the structure.
But... I would still recommend it over nothing. I would prefer a retreat that had the structure and setup but without the dogma. If you cannot find such a place nearby (Goenka's retreats are everywhere), well just know going in that you will need to deal with all this and ignore the dogma and not be upset. Consider it additional training. Maybe try hanging out with people praising homeopathy and not saying a single negative word as preparation for the kinds of things you're going to feel?
I would also note that Sam Harris's guided meditation (https://www.youtube.com/watch?v=OboD7JrT0NE) was quite instructive, after reading his book. You do not have to buy into his overall views or be "a proud atheist" to enjoy the book nor his meditation part.