Flagging, Prioritizing, Categorizing, Dates (Start & Due), My Today
Outlook's To-Do feature (flagging) affects Tasks, Mail, Contacts, Calendar...everything in Outlook.
Each item in Outlook be it a Message, Task, Contact, Calendar entry, etc. could be managed more effectively were the following allowed to be applied to any Outlook item:
4.) Dating (start and/or due dates)
5.) Add a “My Today” field/button (not a date)
Again, the above five items are the core of what makes Outlook amazing. These should be easier to apply regardless of what Outlook item is being worked on in the web app or desktop app, period.