The Nexus Player is simply the Nexus/Android version of the Apple TV, though the open nature of Android means there are a lot more apps that the Nexus can use. I've been using MediaBrowser for years (similar to Plex or XBMC), because I prefer the interface and the metadata features, and I nearly bought a Roku 3 when a client for MediaBrowser was released for it, but I held off, waiting for the Android TV, and now I'm glad I did.
Of course, as I've been saying for years, Android TV needs to have Hangouts support, and I'm still hoping that it will come, though perhaps on a third-party device. I'm still surprised that a USB webcam and Hangouts support isn't an (extra-cost) option.
Still, I'll be getting a Nexus Player in the next month.