It looks like it hasn't been mentioned in a while, but the font size for both the windows app and the Outlook plugin needs to be adjustable. It doesn't seem to respond to the font scaling in Windows 8.1, and on a high res screen (2600x1440) it's too WAY small to use for me. I simply can't use Todoist on my laptop.
Also, to be clear, I'm not looking for a native Windows 8.1 app. I use desktop mode.