Two things sold me on this superb device: remote control and Google Music. The remote controls for Roku and WD Live are just awful. With Chromecast your remote control is your smartphone (Android or iPhone), tablet, or computer. No more agony of scrolling thru lists with up/down arrows. And Google Music seems better than Pandora (although more expensive), because I can upload my own music and I can play entire albums that I don't even own; in addition, GM has the "radio station" features of Pandora.
One other thing I've used it for was to watch a show on Xfinity (if you're a Comcast subscriber). I started the video on my computer, full screen, clicked the Chomrecast button, and there it was on my TV. Audio quality excellent, video seemed a bit better than standard def.