Though I'm sad to see GR disappearing, the primary reason for not using GR for me in the past 3 months has been because of Prismatic.
I've tried a NUMBER of content aggregators, content discovery tools, social feeds (whatever you call it) because I do like finding good reads, so far I think Prismatic team has very closely 'got it'.
It's by far the more accurate "we will find articles that you would be interested based on your taste" tool from my opinion.
I imported my Google Reader data (or so I am led to believe), but all I see is a generic feed full of (admittedly interesting, but not what I want) generic news stories. I see a way of adding 'interests' but not 'feeds'.
My confusion is somewhat assuaged by the awesome '/people' page.
Is this a Reader replacement, or a Reader poaching?
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[edit: I see that this tool does not include an RSS reader, which I thought it would based on the invitation screen. This does not do anything that I use Google Reader for... which is to read RSS feeds!]
As far as the website goes, the home page feels way to cluttered and it's not always clear what the elements do. For example, the purpose of the bar on the right isn't immediately obvious, and interaction with it isn't very intuitive - it looks like it scrolls vertically because of the cut off suggestion at the bottom but actually slides horizontally using buttons.
When it comes to discovering new topics I think a more interactive and transparent method than the suggestions box would be useful. I would love to have a graph/web of topics clustered around my interests that I could browse. I would also like to search for topics and see how they fit into the graph and related searches.