Right now, Google Tasks feel very simple (which may be by design or because they needed some app for tasks really quickly) and it lacks many features like repeated tasks, subtasks, priorities, sharing etc.
It feels that the current implementation is really meant to run as a sidebar in Gmail / Calendar though a full-screen version exists (https://mail.google.com/tasks/canvas).
There was a blog post a year ago that suggested that Google will work on new version of Tasks but I haven't seen any improvements for a long time. Does someone know if they are working on it?