The Chromecast has been very successful since it went on the market in July 2013. Initially, it sold out very quickly, and the availability of a limited Netflix promotion (three free months of service) ran out within a few hours of launch -- the device wound up on backorder for up to three months for some purchasers. By the end of 2013, Chromecast was readily available from retailers.
Reviewers praise the device for being one of the cheapest streaming options, for ease of setup, for working quite well via its supported apps and for its unobtrusive form factor that allows it to hide behind your TV in most cases. It does require a power cable, however, which can make it a slightly awkward addition to your home entertainment system, although it does avoid adding a new box to your collection.
Its Chrome browser tab mirroring functionality gets some criticism for poor picture quality and technical glitches, although that feature was still in beta as of early 2014. The strength of your WiFi network can also affect Chromecast's streaming picture quality. Some users experiencea lag of a few seconds between casting media and when it actually plays. And if you don't have a compatible client device running a supported OS and a compatible router, you're out of luck entirely.
Because any compatible device on the same network can control any Chromecast on that network, multiple devices can interfere with each other. The last one that tries to play a video or music or cast a tab to your Chromecast will win out. This might not be much of a problem on a home network, unless someone unintentionally casts something they wouldn't want their family or visiting friends to see (or if you live with a jerk).
The only real security is your WiFi password, provided your network is password protected. Anyone with this password can stream through the Chromecast. But as of January 2014, the only authentication information it prompts you for is your WiFi password, so you may not be able to use it with WiFi networks that require other information, like corporate sites that ask for a username or hotels that ask for your room number and name.
So far, Chromecast has far fewer channels available compared to other streaming devices on the market, which isn't terribly surprising since it is the new kid on the block. Google plans to release the finalized SDK and to launch the device outside of the United States in 2014. Wider availability and access by more developers should lead to a much larger number of Chromecast-compatible apps over time. And once the device's ability to run things from a Chrome browser tab comes out of beta, the sky might be the limit as to what it can stream.