Considering that since it is a mobile version, the approach should be slightly different from the web version:
- Dashboard centered. The main screen should have a summary of your stuff e.g. your questions, your answers, notifications, etc.
- When you're on the question browsing view, the capacity to toggle between the most relevant questions and all of them should exist.
- maybe a 'favorite categories' preset view could be useful so you don't have to see all of them on your phone.
- an refresh rate setting so you don't suck up bandwidth you don't need to.
- clean UI over flashy stuff. always.
- free, of course
hmmm... plus all the 'by default' UX stuff that normally make apps not suck.