Earlier quoted context omitted.
Genuine question -- how how is it been a revelation? It seems to be very similar to HipChat, which was just an iteration on previous chat systems.
The difference is people like using it. UX counts for a lot. The massive amount of integrations for it helps a lot too. Their goal, from what I've read, is to be a giant log for everything in your company, not just a chatroom service.
There are parts we don’t like about Hipchat (the shortcuts for the emoticons are just weird), but we are using it company-wide where Slack was just used by developers (and Hangouts was used by everyone else).