They communicated the vision really well. Better pricing too. I think, strictly feature wise - search was the only differentiator.

At the time we were using the rather obscure Flowdock[0]. Didn't feel like switching. Felt mostly the same. Before you know everybody was talking about Slack. Everybody understood the value of team chats. They made the competition irrelevant before anybody even cared to look for alternatives.

[0] have to mention the great support though, helped us a lot even as an unpaying customer