As an starter It has to solve a problem or enjoy.
Besides that there are some app mechanics that I will expect when heading for the summer 2011:
- Single Sign-On via Facebook – other login providers as twitter and linked in as option
- Local and connected – it must be usable without connection
- Fast – blazingly fast; loading fast, has a fast internet connection and does stuff without waiting
- Use both shake, swipe, maximize and minimize gestures
- Use sensors as camera and GPS
- Pleasant graphics
Do you think it is too much? Or do you have other requirements?