Some of Play's promise sounds reminiscent of my6sense, the digital intuition iPhone app I help to advise as part of Paladin. Brian Shih, product manager at Google Reader, explained that Play watches your behavior, and tailors itself to your own personal interests.
One Item (A Video) Displayed In Google Reader Play
"As you browse, let us know which stuff you enjoy by clicking the "like" button, and we'll use that info to show you more stuff that you'll like," he said in an e-mail. "If you want, you can also choose categories and we'll personalize your stream to only show you stuff from those categories."
The technology behind Play has been publicly available in Reader for some time, including the same code behind "Recommended" items and sources, as well as the sorting function they call "Magic". While you don't need a Google account to use Play, if you do sign in, it will be personalized with items that you already like, including items that people you follow in Reader have shared, as well as other items similar to those things you have taken action on before.
One Item Displayed In Google Reader Play
Shih says by no means is Play intended to replace Google Reader outright. He says "both Google Reader and Reader Play are about finding and reading interesting stuff online". Play is supposed to be, yes, more fun, while Reader is all about organization, tracking your history and making sure all your items are read. From within Reader, you can view any feed in "Play" by opening the feed settings and opting to "View in Reader Play". (See image on left)
Disclosure: My6sense is an assumed competitor to some aspects of Google Reader, and My6sense is a Paladin Advisors Group client, where I am managing director of new media.