Don't call it a YouTube replacement--users can't upload their own videos, for starters. And while there is a search box, that's not what drives the app. It's more of a channel-surfing engine--you just swipe around and check stuff out. The videos autoplay, and you can swipe up to change channels or swipe forward to get a new video.
The navigation feels much more natural by result. Tapping on YouTube videos seems so choosy by comparison: you're picking one thing. I want to watch...this. Swiping feels like you're just flipping through channels with a TV remote: next, next, next. Instead of choosing one thing, you're just asking the app to show you "something else," and then you can decide if you like it and want to finish watching it.
Aside from the self-explanatory Popular channels, the others include classic Saturday Night Live clips and, thanks to a new content partnership with Viacom, a Comedy Central channel with clips from The Daily Show and The Colbert Report. The rest of the lineup includes The Onion News Network, Comedy (which features Yahoo original shows like Tiny Commando), Vogue, Celebrity, PopSugar, ABC News, GQ, Wired, Mansome, Food, Martha Stewart, Gaming, Movie Trailers, Sports, MLB highlights, UFC, and even a whole channel for fantasy football.
You can get more info on a video by tapping the arrow by the playhead, and since Web video is made to be shared, you'll find options to do so via Facebook, Twitter, and email.
But the rest of the time, the interface fades away and you're left with just auto-playing video and tons of it--Yahoo says the comedy videos alone total more than 1000 hours. The swipe interface is a snap, but some of the icons used to denote channels aren't instantly recognizable, and it'd be nice to be able to save videos as favorites.
Yahoo Screen is a free download for iPhone and iPad, but it isn't yet available for Android.