The Apple TV embargo lifted last night, and the first reviews have been published with a general consensus that the device is a worthy upgrade with some annoyances for search and logging into apps.
I recommend starting with Christina Warren's review, which gives a great overview of the platform and the brand new Siri remote:
Swiping faster on the touchpad moves faster across the interface, slower goes slower. Movements are extremely precise and never felt out of control. The remote is Bluetooth — not IR — so you don't need direct line of sight to navigate — which is nice. On some Bluetooth-based remotes, I've noticed lag between a selection and what happens on screen but the Siri remote always keeps up.
Tapping the Menu button will take you back one level or give you a menu of an app you're in. Tapping the home button will bring you to the core home screen. Double tapping the home button opens up an app switcher, so you can easily navigate between screens. If you want to close out an app, swiping up on the trackpad will dismiss it.