Google's Nexus Q was supposed to be the thing that legitimized Google TV, taking it from comical TV feature to a fluid addition to Google's services. Instead, it flopped, then never even came out. So Asus decided to make its own streaming box.
The Qube's big feature seems to be its motion sensing via an "advanced remote control", which is used to manipulate the interface on "a rotating on-screen cube shape" on the screen. It also uses voice control for navigation and search, and sort through Netflix and Amazon Instant Video movies and TV shows. It'll also play games and apps from the Google Play store. That means it's already got a leg up on Apple TV—one of its main competitors—by being open to the app store.
There's also a Mobile Remote app for Android phones and tablets to control the Qube, but we want to see how that holds up under daily use, since those tend to be pretty finicky (e.g. Microsoft's SmartGlass).
The reason boxes like the Qube or the Nexus Q are so promising is that Google TV's been practically begging for a successful external device to put it on any TV with an HDMI port, instead of being confined to only those TVs it's preloaded on. This should help along wider adaption, which in turn would help improve content. And Asus being first out the gate, before Nexus Q relaunches (f ever), would imply that there will be a lot of these coming. That'll be a fragmented headache for us, but it's the approach that made Android as popular as it is today.
We'll let you know as we have more details about the Qube, but for now, we're hoping there's finally a reason for most of us to use Google TV.