It's possible that you don't personally use all the features of Google Reader, but AFAIK, Google+ lacks one of the most basic (and, IMHO, useful) features of Google Reader: the ability to maintain the state of read/unread articles. Not to mention that the Google Reader's API makes this state available across multiple devices.

If Google+ can't manage this fundamental task, it will be a fail (to me) as a replacement for Google Reader. But I don't think replacing Google Reader is Google's goal; if it were, it might have been better for Google to build Google+ on top of Reader than to try to recreate all the Reader functions into Google+.