Although it was great and somewhat novel, when Chromecast was launched it had limited functionality and was pretty much locked down. Although it has been freed-up a bit as expected, this has been fairly slow and mainly limited to specific apps.
Now Google has announced that CC will be able to mirror any Android device without apps needing to have CC support - a long-awaited breakthrough:
http://www.androidcentral.com/chromecast-mirroring-will-blast-any-android-display-big-screen
Huzzah!