Redundancy
A feed reader shows you the latest information from each site you've subscribed to. Often, many blogs discuss a single news, but you don't have all these posts at a glance. A feed reader should cluster related posts.
Closed universe
You have a list of feeds, but you can't discover new feeds organically. Your list of feeds should automatically based on your preferences.
Lack of order
There's no hierarchy in your feed reader. You may have only 5 minutes to find out what's new, but you don't know where to start. A good feed reader should rank posts and prioritize breaking news.
Sense of guilt
If you don't open/visit a feed reader for a week, you may end up with hundreds of thousands of unread posts. You may want to mark all as read and move on, but what if you lose something important? A feed reader forces you to read (or scan) each and every post.
No related universes
Maybe there are other people with similar tastes that may help you improve your universe. A feed reader should automatically detect that and suggest posts that were considered interesting by your virtual group of anonymous friends.
In most of these affirmations, I've described a typical feed reader. If you know one that does all of these things (or only some of them), let us know.