DA has always had a culture of being a safe place online to post something you've made without fear of ridicule. I joined in 2001 as a person-who-liked-drawing but had no scanner, so I tried out writing, since that was a category on there that other people were doing, and I got terrific feedback from a handful of strangers, who quickly became friends. Now I consider myself a writer. Programmer/writer, but writer nonetheless, and I don't think that would have happened without DA. I eventually became a programmer there for a while too, so maybe I wouldn't have become either of those. ;)
Anyway, as far as I could see, that welcome-to-the-community experience was happening to everyone who joined, if they were participating at least. It's bigger now, so it's hard to bump into the right people when you're new, but that same DNA is still there. Read the comments on any popular piece - it's usually positive and constructive. And often extensive.
I don't know if I'm replying well; I feel like this ultimately just sounds like "you had to be there" - but when it comes down to it, I believe the amazingly positive culture is the answer to "what was amazing?"