Overall, Material's interface is well designed, with lateral and vertical swipe gestures to go between stories and categories. The category screens are nice, with full-width images and bright colors. And the popped-out story pages give you a no-frills view of stories, similar to what you would see in an RSS reader app like Feedly. You can even jump to a full Web view of a story by hitting the double-arrow button up top, and you can share a story via Android's Share protocol.
As for the content itself, Material's algorithm did a good job of predicting my interests. On Twitter, I tend to follow people who are into technology, basketball, film, and comedy, and those topics are well represented in my daily digests. I did see some glaring holes in my coverage, though, so I had to manually add in the topics that were missing. Also, I had to delete a topic -- football -- which I don't normally read about (but apparently my Twitter friends do). What's important to remember is that results here may vary, depending on how accurately your social data reflects your personal interests.
One of the problems I found with Material was that it regularly included several redundant stories in my news feed, which was annoying. With each category containing up to 30 news stories, I would sometimes see five or six of the same story (from different sources) within a single category. The good thing is that I did notice a diversity of news sources populating my feed, so, even among the redundancies, I had an opportunity to discover lots of new content that I otherwise might have missed.
Also, I was disappointed to see that there is no way to revisit a previous digest. It's probably not necessary to be able to reference all of your old digests, but it would be nice to be able to at least step back to your Morning Digest, even after you've opened your Afternoon Digest. Maybe we'll see that feature added in the future.
And finally, Material seems to be troubled by a number of bugs. On several occasions, I saw the app freeze for a second and then shut down. Hopefully, because the app is still new to the market, Material's developers are working on fixes. But for now, don't expect it to perform all that reliably.
Material will likely be an attractive option to those who don't want to put too much work into a news reader like Flipboard. With an exceptionally low barrier to entry, it asks you to simply sign in to your Facebook or Twitter account, and from there, it will autodeliver personalized digests of news stories twice a day. The app's interface is well designed, and it has wide images and bright colors, which give it an altogether modern look. It could use some additions like the ability to see old digests, but otherwise the feature set seems pretty solid.
Where Material really falls short is performance. It does a good job of homing in on interests, but the technology could improve its accuracy even more. Within your feed, it would also be nice if there weren't so many redundant stories. And of course, the biggest area in need of improvement is Material's stability. With all the freezes and forced shutdowns, we can only hope that this app's developers are planning to pump out the updates sooner than later.