It started with just gaming content and has lately evolved into a lot more like creative content and streamers just streaming about their life in the "IRL" section
Which is an interesting recursive evolution considering that Twitch was an evolution of gaming being the most popular vertical on Justin.tv.
Justin.tv started with only one channel, a 247 broadcast of the founder Justin's life. Many additional early channels also revolved mostly around lifestreaming but quickly the site saw more categories, gaming being one of the more popular ones.
I've always said that the Internet is recursive.