The top three things a server to do.
First and foremost the server should do what it is supposed to do. Say if you installed Samba Active Directory, and Active Directory should be there and acting like it should do.
Second, backup/restore and backup/restore and backup/restore. Backup/Restore should work and if not working, do virtual and backup the virtual.
Third, almost tied to backup, is documentation. Documentation is everything. If everything is not in documentation (or someone misinterpret what it said) they might mess the server up, and they might have to go to backup. If restore is not working, I hope they are doing virtual and backing up the virtual.
This is a tall order.
Editing: Changed the Backup to Backup/Restore.