Microsoft To Do has so much potential but lets me down in the following ways:
custom list don't show up in Outlook tasks.
Can't share task individually or the whole task list unless it's a custom list.
No dashboards like Planner
No way to bucket task which is helpful for work.
No way to export list to excel without regular copying and pasting (but at least you can copy and paste)
No way to connect related task except as links
The only way to add categories is in Outlook or using a hashtag but they act and show differently so you have to pick which one to use or use both separately.
These issues wouldn't be so bad if you could use Planner instead and have Planner task show up on your MS Outlook task list. You can't plus Planner doesn't allow you to connect related task. Grrr if Microsoft would just create a combined version of Planner and To Do with the ability to create related task that would be great.