You make a good point about all the integrations. I might be in an minority situation, but none of the people who are enamoured with Slack that I work with are

You make a good point about all the integrations. I might be in an minority situation, but none of the people who are enamoured with Slack that I work with are using any of that stuff. It's just instant messaging with a sprinkle of file sharing to them. It seems to me the biggest thing, as others have pointed out, is the polish and the native apps. For example, Hangouts does most of it, but Google has killed of their native apps and the in-browser experience is really suboptimal. Having a simple, dedicated, well designed native app really makes a difference.