Tangentially, it saddens me to see people forgetting about simple native desktop apps - no getting shut down; no ads; no obnoxious social bullshit; just simple tools that succeed based on being useful rather than getting their users hooked and spamming their contacts for attention...
Unless it also has a mobile app that syncs what I've read with the desktop app, it's sub-par to Google Reader for me personally. This is actually the most important of any feature for me.
I need to be able to go back and forth between desktop, laptop, and phone and never lose my place. I travel, co-work periodically, and like to read my feeds over lunch on most days.
One thing which I've found rather irritating with Windows 8 and Windows Phone 8 is you find a great RSS app like Feed Monster, but then its not available on the WP8 platform. I'm constantly finding good apps for the desktop which are not available on the mobile platform and its incredibly frustrating. Add then you have some great apps like Feedly which are not available yet on WP8 (and probably won't be).
I'm pretty sure I'll be moving back to Android at the end of the summer.