There are many things I like about Unraid, but the most would be how easy to use Unraid is and if something isn't available through the GUI you can with the terminal.
One thing I like to see added to Unraid is more overview in CPU, RAM and Network live and past usage (natively in Unraid instead of a Docker) for each VM and Docker.
Else would be a cluster like setup so VMs and Dockers can be (live) migrated to other Unraid hosts.
PS, Snapshots would also be nice within the GUI 😉