I like Prismatic a lot, and used it more than a few times a week. From the user perspective, here's where I think they failed to execute well.

1. They did almost zero marketing of the product. Almost of their marketing was based around their engineering prowess (maybe this was by design).

2. The sites they scraped and indexed for content were largely B and C grade. For example, I never saw content from the NY Times. Google News scrapes this site, so from a disappointed user perspective I chalk this up to laziness on Prismatic's part.