Picked up a ShieldTV last week and so far I'm impressed with it functioning as a media streamer with Plex and Emby. It definitely replaces my Raspberry Pi 2 running OpenELEC and lumps everything into one box. Plex for local media and Emby for remote live TV watching.
Most everything I have it plays directly through Plex. If it has to transcode, it's usually only audio. HDMI-CEC lets me use my TV remote to control it. Nvidia streaming lets me use the ShieldTV similarly to how I use Steam in-home streaming. Oh and the UI is blazing fast. This thing does it all, quite well!
All that aside, I can now say I've ditched Kodi and moved exclusively to Plex. I hated the inconsistency of watched flags for my media with having Plex on mobile devices and Kodi on my media box, so having the ShieldTV which provides a great Plex UI helped make that decision.
However, until Plex gets better channel support for devs to make some better looking UI's, I use Emby for streaming live TV from my office (have a PC there that has a Ceton card + ServerWMC) because having the full guide looks a whole lot better than a text-based menu.