Decent, can play in background unlike YouTube, but... – Twitch: Live Streaming Review

You should fix the issue where if a streamer goes offline during a stream it won't automatically reconnect you to them when they come back. The only way to get them back on your device is to go into to the quality settings, set it to Chat Only, then disable Chat Only. That, or exit their stream and re-enter, which then can take upwards of 30 seconds if an ad starts playing again.
Review by Zai Redwinters on Twitch: Live Streaming.