Improve communication during service outage.
I find the lack of clear communication during the recent service outage severly lacking. I'd expect close monitoring after such a major infrastructure update, but still there's a huge delay between global problems preventing play and an update in your status page and official forum thread acknowledging the problem.
During the several hours in between, your users will try to troubleshoot the issue on the client side while for you it's clearly on the server side. You're wasting all your players' time by not timely updating your status page and forums.
You should seriously prioritize monitoring and communication. You can't prevent all issues, but you can do a lot to find them and communicate in a timely manner.