I would really like to see Opera Sync support syncing the full browsing history between devices similar to Firefox and Chrome. Currently, Opera only syncs a list of web addresses that are typed into the address bar which are auto-completed on other computers. That is not that useful and somewhat misleading when they advertise history as a syncing option.
It is very useful to be able to look back in history to find a web page that I previously visited. I greatly enjoy using Opera, but until that history is synced across multiple devices, I cannot fully switch away from Firefox.