[replax]

From the screenshots I'd say that you are talking about a Desktop/Web application?

In that case, It'd have to be significantly better than e.g. Google Reader (which got a little crippled unfortunately). Personally, some of the most important features would be, that it has colour schemes (e.g. like the Vim Solarised scheme) and allows offline caching/easy, good e.g. pdf export.

However, I have to admit that a decent mobile (iOS, WP7, etc.) Application would be of much greater interest to me, as that is where the advantage of a RSS reader significantly comes into play due to the much more limited screen estate.