NancyatMSFT Thank you for taking the time to engage with us. For me, as of now, I see at least two major issues.
The first one is that To Do’s features aren’t completely replicated in Planner. For instance, there’s no hierarchy in lists and folders, list folders aren’t present, etc. I’m assuming it’s on the roadmap, but I think Planner needs to replicate 1-to-1 To Do’s features to make it work.
The second issue is not directly related to features, but instead of the way Planner tries to treat To Do and plans similarly, albeit they’re different things. Task lists from To Do are treated as plans, but they’re not. Plans are sort of forced into To Do, but maybe they shouldn’t. The overall experience is very confusing, it feels like we’re using a weird hybrid that is not as simple as To Do, but also not as powerful as Planner.
A final issue is that tasks with due dates should appear in the calendar in Outlook. Not in a sidebar, but directly in the calendar, alongside events. Apple will soon ship a similar integration between Reminders and Calendar, Microsoft should do the same. (I know there’s a workaround with iCal feeds, but it’s a very subpar experience; what I’m referring to is a native, first class integration between tasks and events in a unified calendar view.)
Hope it helps. I can elaborate if needed.