We made the switch last year; here's our
transition thread. We tried very hard to respond to every comment, and used
Iversia's FAQ manager for common questions. If a problem could be fixed fast, we did it. We implemented as many reasonable suggestions as we could, as quickly as possible. For people that were really struggling, we started a private conversation to walk them through using the site. We have many ESL members and quite a few who aren't tech savvy at all, so some people needed extra help. Overall it went well, but it did involve answering lots of questions and making many little tweaks.
Here are some things people just couldn't warm up to:
• not having folders for watched threads (we had to commission an add-on for this)
• 'friends' becoming 'followers' rubbed some people the wrong way
• avatars in the thread list
• some differences in elasticsearch vs sphinx
• the reports area got a mixed reception from staff
• the forms add-on we used in vbulletin is better than anything that exists for xenforo
However, we get new members every day. Almost a year later, plenty of people have no idea what the site was like before. If we were to magically replace xenforo with the old vbulletin site for a day, I think people would be appalled. XenForo is far superior to vBulletin in most ways, and I think most people can see that.
The best advice I can give is to keep your own attitude upbeat and take the criticism in stride. Believe me, I know how hard you worked on this, and how tough it is to face criticism after all that work. But if you read transition threads on other forums, you'll see that yours is perfectly normal and not overly negative. Make sure staff don't 'fight back' but just thank members for their feedback, reassure them and make them feel heard and valued. Ultimately their feedback makes you stronger, so hang in there!