MS ToDo could be a great task tracking app. It has a lot going for it - it's free, cross platform, and integrated with Exchange. Unfortunately, the implementation of some of it's features is so poorly executed, it's really undermining what could have been a killer functionality.
Top two issues:
1) The # tags could be incredibly powerful. They are easy to apply on the fly, and easy to use by simple click. They can be used in email subjects and Outlook tasks. Unfortunately, when you filter by tag, the resulting list is not arranged by due date, making it useless. I can't click on #Milestone and get a "big picture" overview, and I can't click on #VendorABC and get a list of things that this vendor owes me arranged by due date so I can immediately see which ones are behind and which ones are coming up. The resulting list is a pile of dung with dates all over the place, that is only good for giving me headache when trying to make sense of it. So, here goes one killer feature.
2) The iPad and iPhone apps are way behind W10 app. I can't even have tasks from two different accounts, so if I am tracking my work tasks I won't get notifications about my personal tasks, forcing me to use some other task manager for that. Seriously, MS, do you really want to deliberately push your users towards competing products? Because that's what you do.
There's more, but these are two top most annoying issues....