What made Google Reader more important than similar services, was that other products were also able to access Google Reader though it’s API. That way Google Reader became part of the backbone of many other online news services. It meant that, instead of you having to maintain your RSS feeds in multiple products, all these services got the information from Google Reader where it was stored.
At the moment, the most promising replacement for Google Reader seems to be Feedly. I’ve been using Feedly for a while and like it even though there are some bugs. Feedly has now promised to help Google Reader users migrate to their service and to open their service to other’s so that they could become the new backbone for RSS driven services. I wrote abut Feedly and similar products I rely on to find interesting news in a post last summer.