We used it from 2007 to 2016, the transition was smooth, and only a small percentage of members complained about Discourse. BUT once they were used to Discourse and how to use its feature, they never wanted to back to VB.
What most of them were missing was the VB homepage with listed forums and subforums, and pages in threads. Over time that faded and we can hear about it only when new members coming from ‘classic’ forums join our Discourse powered board.
That being said, I can’t think of any feature that I’m missing from VB that is not already part of Discourse. I think going back to vBulletin from Discourse would be a huge step back.