You can get a perspective on various eReader devices by checking the articles below:
1OTA Support: the ability to access and download content, over-the-air (wirelessly).
2Effective Navigation: an intuitive and simple user interface for navigating through books & content.
3Non-flicker screen: an eINK (or similar) display for a paper-like reading experience. Colour would be nice.
4Long battery life: a battery life of many thousands of pages/downloads - plus rapid recharge capability.