In principle, I agree in most arguments for the removed features. It makes the GUI much more clearer to use.
But I cannot accept the removal of mailbox rights tab. We make heavily use of granting send-as rights to functional mailboxes. For the guys in our accounts management team, the new shell (which I like) is not adequate.
Also missing is the public folder management option. Although you are going to phase out public folders, there are still a lot of customers who had applications built on them. Until they migrated public folder to something else, public folder have to be managed.
Whats about the ability to monitor current logon connections to mailboxes; I didn't find anything to do this task, neither in the new GUI nor in the shell.