I am adding this suggestion of "simplicity" to explain that my reason for using ToDoist is its simplicity.
I, too would like a few additional features, but I want it kept clearly in mind that the greatest benefits of ToDoist are its simplicity and its availability on many platforms.
If you're in need of a fully blown project management system, there are many great ones out there.
What isn't out there, other than ToDoist, is a simple to do list system which is multiplatform and integrates with things like Thunderbird. In fact, integration with Thunderbird to turn emails into tasks is one of the main reasons I decided to give ToDoist a try.
So, I'm voting as a reminder that the best thing about ToDoist is that it does KISS (Keep It Simple Stupid) really well.