I went from a HTPC to a WDTV and was pretty happy for awhile but decided to go back and build a HTPC/NAS box that runs 24/7.
XBMC, Sabnzbd, Sickbeard, Torrents, Hulu, Transcoding/Stream with AirVideo, on Iphone/IPad.
If your sole purpose is watching video, I think for most people a all in one device that's $70-150 is better suited.