I am an avid GTD enthusiast (Getting Things Done, by David Allen). Two items of note, I use Outlook both at home, and at my work, both using the MS Office 365.
1. My office does not even show the To-Do sidebar. I assume the IT Department implementation blocks it from being implemented.
2. My home "Office" does show the To-Do sidebar. I became aware of To-Do through instructions provided by GTD called "Outlook Integration", where they relied heavily on the To-Do feature. I thought this is my solution! But, sadly I find it's functionality too limited to be of real use to me. I read with interest the previous posts from others more technically savvy than me, which I fully agree with.
I will be monitoring any future updates and releases, hoping they may address the shortfalls. But for now, I will be relying on "One Note" as the hub of my GTD. Not Outlook, until there is a more seamless integration for my tasks, projects, and reference files (I have a LOT).