Overwhelming is the right word for sure. It's awesome to experience something like breakthrough, but what could one bring back?
I have a number of experiences that are fun to remember, but they were too out there…
why do you not consider that itself as something brought back?
I used to listen to the new atheists and the scientific skeptics, Seth Shostak's Big Picture Science podcast, the guy behind the SETI Institute (the Search for ExtraTerrestrial Intelligence), etc., and apparently none of these people who devote hours of their life every week to the subject of life beyond Earth, intelligence superior to ours, worlds that are more beautiful and harmonious than the one we're at times building and at times destroying, have ever had enough curiosity or courage to take one deep breath and see for themselves what's down the rabbit hole.
For me, that glimpse changes everything. I may not be able to draw a cool picture of what I saw. I may not be able to convince you that what I saw was more than my imagination (though I do believe there are some experiences which are more plausible on that model than on the materialist model, which are sufficient for the experiencer, though not sufficient for the rest of the world who can only trust or doubt their story). But I can never go back to looking around and thinking this house and this city and this society is the only interesting one to explore. I can never go back to laughing at people praying to their god as if they're credulous children following fairy tales and believing in magic.
One thing I brought back was the knowledge that 'the third eye' is real. whatever it means that it's real. Even if it was only a window into your own mind, your own private imagination, well, I thought there were only walls there. I thought no one could see any such thing, whatever such things are. I had no idea I could dream up such wonderfully complex ecosystems of joyful activity and strangeness. I really don't think I can. Whoever believes it's all in their head must see some incredibly boring and ordinary things, or have an exceedingly high opinion of themselves.
Even just the knowledge of what my mind is capable of seeing is something I bring back with me. I stare at a tapestry on my wall and it looks random and confusing to me. I can't see what the artist must've seen in choosing to draw it that way. then after a deep breath I can see it shift and fragment into layers that all make beautiful sense....for a few short minutes before that enhancement of my perception fades and I can only perceive it crudely and flat again, like someone temporarily given color vision to see a rainbow or a sunset and then gone colorblind again. To know that is possible is something I brought back. To know that technology exists, and that we walk around every day trying to achieve things and taking risks based on our limited perception, when very easily improvements to it are possible but forbidden, I brought that back with me. It's like having had depression and then getting serotonin and going 'oh, is this why everyone else doesn't want to kill themselves? is this how they get up and go to work every day so easily? this is much easier, this is much better! this might even be fun!', knowing the radical contrasts in human experience and capability can be mediated not just by the luck of genes or decades of study and personal development, but by a deep breath of the right molecule? I feel like that should be front page news.